Plants having altered agronomic characteristics under nitrogen limiting conditions and related constructs and methods involving genes encoding lnt2 polypeptides and homologs thereof

ABSTRACT

Isolated polynucleotides and polypeptides and recombinant DNA constructs particularly useful for altering agronomic characteristics of plants under nitrogen limiting conditions, compositions (such as plants or seeds) comprising these recombinant DNA constructs, and methods utilizing these recombinant DNA constructs. The recombinant DNA construct comprises a polynucleotide operably linked to a promoter functional in a plant, wherein said polynucleotide encodes an LNT2 polypeptide.

This application is a Divisional of U.S. application Ser. No.12/741,384, filed May 5, 2010, now Allowed, which is a 371 ofPCT/US08/82421, filed Nov. 5, 2008, now Expired, which claims thebenefit of U.S. Provisional Application 60/986,088, filed Nov. 7, 2007,now expired, the entire content which is hereby incorporated byreference.

FIELD OF THE INVENTION

The field of invention relates to plant breeding and genetics and, inparticular, relates to recombinant DNA constructs useful in plants forconferring nitrogen use efficiency and/or tolerance to nitrogen limitingconditions.

BACKGROUND OF THE INVENTION

Abiotic stressors significantly limit crop production worldwide.Cumulatively, these factors are estimated to be responsible for anaverage 70% reduction in agricultural production. Plants are sessile andhave to adjust to the prevailing environmental conditions of theirsurroundings. This has led to their development of a great plasticity ingene regulation, morphogenesis, and metabolism. Adaptation and defensestrategies involve the activation of genes encoding proteins importantin the acclimation or defense towards the different stressors.

The absorption of nitrogen by plants plays an important role in theirgrowth (Gallais et al., J. Exp. Bot. 55(396):295-306 (2004)). Plantssynthesize amino acids from inorganic nitrogen in the environment.Consequently, nitrogen fertilization has been a powerful tool forincreasing the yield of cultivated plants, such as maize and soybean.Today farmers desire to reduce the use of nitrogen fertilizer, in orderto avoid pollution by nitrates and to maintain a sufficient profitmargin. If the nitrogen assimilation capacity of a plant can beincreased, then increases in plant growth and yield increase are alsoexpected. In summary, plant varieties that have a better nitrogen useefficiency (NUE) are desirable.

Activation tagging can be utilized to identify genes with the ability toaffect a trait. This approach has been used in the model plant speciesArabidopsis thaliana (Weigel et al., Plant Physiol. 122:1003-1013(2000)). Insertions of transcriptional enhancer elements can dominantlyactivate and/or elevate the expression of nearby endogenous genes. Thismethod can be used to identify genes of interest for a particular trait(e.g. nitrogen use efficiency in a plant), genes that when placed in anorganism as a transgene can alter that trait.

SUMMARY OF THE INVENTION

The present invention includes:

In one embodiment, a plant comprising in its genome a recombinant DNAconstruct comprising a polynucleotide operably linked to at least oneregulatory element, wherein said polynucleotide encodes a polypeptidehaving an amino acid sequence of at least 50% sequence identity, basedon the Clustal V method of alignment, when compared to SEQ ID NO:18, 20,24, 26, 28, 30, or 32, and wherein said plant exhibits increasednitrogen stress tolerance when compared to a control plant notcomprising said recombinant DNA construct.

In another embodiment, a plant comprising in its genome a recombinantDNA construct comprising:

(a) a polynucleotide operably linked to at least one regulatory element,wherein said polynucleotide encodes a polypeptide having an amino acidsequence of at least 50% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO:18, 20, 24, 26, 28, 30,or 32; or

(b) a suppression DNA construct comprising at least one regulatoryelement operably linked to: (i) all or part of: (A) a nucleic acidsequence encoding a polypeptide having an amino acid sequence of atleast 50% sequence identity, based on the Clustal V method of alignment,when compared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32, or (B) a fullcomplement of the nucleic acid sequence of (b)(i)(A); or (ii) a regionderived from all or part of a sense strand or antisense strand of atarget gene of interest, said region having a nucleic acid sequence ofat least 50% sequence identity, based on the Clustal V method ofalignment, when compared to said all or part of a sense strand orantisense strand from which said region is derived, and wherein saidtarget gene of interest encodes an LNT2 or LNT2-like polypeptide, andwherein said plant exhibits an alteration of at least one agronomiccharacteristic when compared to a control plant not comprising saidrecombinant DNA construct.

In another embodiment, a method of increasing nitrogen stress tolerancein a plant, comprising (a) introducing into a regenerable plant cell arecombinant DNA construct comprising a polynucleotide operably linked toat least one regulatory sequence, wherein the polynucleotide encodes apolypeptide having an amino acid sequence of at least 50% sequenceidentity, based on the Clustal V method of alignment, when compared toSEQ ID NO:18, 20, 24, 26, 28, 30, or 32; (b) regenerating a transgenicplant from the regenerable plant cell after step (a), wherein thetransgenic plant comprises in its genome the recombinant DNA constructand exhibits increased nitrogen stress tolerance when compared to acontrol plant not comprising the recombinant DNA construct; andoptionally, (c) obtaining a progeny plant derived from the transgenicplant, wherein said progeny plant comprises in its genome therecombinant DNA construct and exhibits increased nitrogen stresstolerance when compared to a control plant not comprising therecombinant DNA construct.

In another embodiment, a method of evaluating nitrogen stress tolerancein a plant, comprising (a) introducing into a regenerable plant cell arecombinant DNA construct comprising a polynucleotide operably linked toat least one regulatory sequence, wherein the polynucleotide encodes apolypeptide having an amino acid sequence of at least 50% sequenceidentity, based on the Clustal V method of alignment, when compared toSEQ ID NO:18, 20, 24, 26, 28, 30, or 32; (b) regenerating a transgenicplant from the regenerable plant cell after step (a), wherein thetransgenic plant comprises in its genome the recombinant DNA construct;and (c) evaluating the transgenic plant for nitrogen stress tolerancecompared to a control plant not comprising the recombinant DNAconstruct; and optionally, (d) obtaining a progeny plant derived fromthe transgenic plant, wherein the progeny plant comprises in its genomethe recombinant DNA construct; and optionally, (e) evaluating theprogeny plant for nitrogen stress tolerance compared to a control plantnot comprising the recombinant DNA construct.

In another embodiment, a method of evaluating nitrogen stress tolerancein a plant, comprising (a) introducing into a regenerable plant cell arecombinant DNA construct comprising a polynucleotide operably linked toat least one regulatory sequence, wherein the polynucleotide encodes apolypeptide having an amino acid sequence of at least 50% sequenceidentity, based on the Clustal V method of alignment, when compared toSEQ ID NO:18, 20, 24, 26, 28, 30, or 32; (b) regenerating a transgenicplant from the regenerable plant cell after step (a), wherein thetransgenic plant comprises in its genome the recombinant DNA construct;(c) obtaining a progeny plant derived from the transgenic plant, whereinthe progeny plant comprises in its genome the recombinant DNA construct;and (d) evaluating the progeny plant for nitrogen stress tolerancecompared to a control plant not comprising the recombinant DNAconstruct.

In another embodiment, a method of determining an alteration of anagronomic characteristic in a plant, comprising (a) introducing into aregenerable plant cell a recombinant DNA construct comprising apolynucleotide operably linked to at least one regulatory sequence,wherein the polynucleotide encodes a polypeptide having an amino acidsequence of at least 50% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO:18, 20, 24, 26, 28, 30,or 32; (b) regenerating a transgenic plant from the regenerable plantcell after step (a), wherein the transgenic plant comprises in itsgenome the recombinant DNA construct; and (c) determining whether thetransgenic plant exhibits an alteration of at least one agronomiccharacteristic when compared to a control plant not comprising therecombinant DNA construct; and optionally, (d) obtaining a progeny plantderived from the transgenic plant, wherein the progeny plant comprisesin its genome the recombinant DNA construct; and optionally, (e)determining whether the progeny plant exhibits an alteration of at leastone agronomic characteristic when compared, optionally under nitrogenlimiting conditions, to a control plant not comprising the recombinantDNA construct.

In another embodiment, a method of determining an alteration of anagronomic characteristic in a plant, comprising (a) introducing into aregenerable plant cell a recombinant DNA construct comprising apolynucleotide operably linked to at least one regulatory sequence,wherein the polynucleotide encodes a polypeptide having an amino acidsequence of at least 50% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO:18, 20, 24, 26, 28, 30,or 32; (b) regenerating a transgenic plant from the regenerable plantcell after step (a), wherein the transgenic plant comprises in itsgenome the recombinant DNA construct; (c) obtaining a progeny plantderived from the transgenic plant, wherein the progeny plant comprisesin its genome the recombinant DNA construct; and (d) determining whetherthe progeny plant exhibits an alteration of at least one agronomiccharacteristic when compared optionally under nitrogen limitingconditions, to a control plant not comprising the recombinant DNAconstruct.

In another embodiment, a method of determining an alteration of anagronomic characteristic in a plant, comprising:

(a) introducing into a regenerable plant cell a suppression DNAconstruct comprising at least one regulatory element operably linked to:

-   -   (i) all or part of: (A) a nucleic acid sequence encoding a        polypeptide having an amino acid sequence of at least 50%        sequence identity, based on the Clustal V method of alignment,        when compared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32, or (B)        a full complement of the nucleic acid sequence of (b)(i)(A); or    -   (ii) a region derived from all or part of a sense strand or        antisense strand of a target gene of interest, said region        having a nucleic acid sequence of at least 50% sequence        identity, based on the Clustal V method of alignment, when        compared to said all or part of a sense strand or antisense        strand from which said region is derived, and wherein said        target gene of interest encodes an LNT2 or LNT2-like        polypeptide;

(b) regenerating a transgenic plant from the regenerable plant cellafter step (a), wherein the transgenic plant comprises in its genome thesuppression DNA construct; and

(c) determining whether the transgenic plant exhibits an alteration ofat least one agronomic characteristic when compared to a control plantnot comprising the suppression DNA construct;

and optionally, (d) obtaining a progeny plant derived from thetransgenic plant, wherein the progeny plant comprises in its genome thesuppression DNA construct;

and optionally, (e) determining whether the progeny plant exhibits analteration of at least one agronomic characteristic when comparedoptionally under nitrogen limiting conditions, to a control plant notcomprising the suppression DNA construct.

In another embodiment, a method of determining an alteration of anagronomic characteristic in a plant, comprising:

(a) introducing into a regenerable plant cell a suppression DNAconstruct comprising at least one regulatory element operably linked to:

-   -   (i) all or part of: (A) a nucleic acid sequence encoding a        polypeptide having an amino acid sequence of at least 50%        sequence identity, based on the Clustal V method of alignment,        when compared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32, or (B)        a full complement of the nucleic acid sequence of (b)(i)(A); or    -   (ii) a region derived from all or part of a sense strand or        antisense strand of a target gene of interest, said region        having a nucleic acid sequence of at least 50% sequence        identity, based on the Clustal V method of alignment, when        compared to said all or part of a sense strand or antisense        strand from which said region is derived, and wherein said        target gene of interest encodes an LNT2 or LNT2-like        polypeptide;

(b) regenerating a transgenic plant from the regenerable plant cellafter step (a), wherein the transgenic plant comprises in its genome thesuppression DNA construct and exhibits an alteration of at least oneagronomic trait when compared to a control plant not comprising thesuppression DNA construct;

(c) obtaining a progeny plant derived from the transgenic plant, whereinthe progeny plant comprises in its genome the suppression DNA construct;and

(d) determining whether the progeny plant exhibits an alteration of atleast one agronomic characteristic when compared to a control plant notcomprising the suppression DNA construct;

and optionally, (e) determining whether the transgenic plant exhibits analteration of at least one agronomic characteristic when compared,optionally, under nitrogen limiting conditions, to a control plant notcomprising the recombinant DNA construct.

In another embodiment, the present invention concerns an isolatedpolynucleotide comprising: (a) a nucleotide sequence encoding apolypeptide, wherein the amino acid sequence of the polypeptide and theamino acid sequence of SEQ ID NO:18, 24, or 26 have at least 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%sequence identity based on the Clustal V alignment method, or (b) thecomplement of the nucleotide sequence, wherein the complement and thenucleotide sequence contain the same number of nucleotides and are 100%complementary. The polypeptide In an embodiment comprises the amino acidsequence of SEQ ID NO:18, 24, or 26, and the nucleotide sequencecomprises the nucleotide sequence of SEQ ID NO:17, 23, or 25.

BRIEF DESCRIPTION OF THE FIGURES AND SEQUENCE LISTINGS

The invention can be more fully understood from the following detaileddescription and the accompanying drawings and Sequence Listing whichform a part of this application.

FIG. 1 shows a schematic of the pHSbarENDs2 activation tagging constructused to make the Arabidopsis populations (SEQ ID NO:1).

FIG. 2 shows a schematic of the vector pDONR™Zeo (SEQ ID NO:2), GATEWAY®donor vector. The attP1 site is at nucleotides 570-801; the attP2 siteis at nucleotides 2754-2985 (complementary strand).

FIG. 3 shows a schematic of the vector pDONR™221 (SEQ ID NO:3), GATEWAY®donor vector. The attP1 site is at nucleotides 570-801; the attP2 siteis at nucleotides 2754-2985 (complementary strand).

FIG. 4 shows a schematic of the vector pBC-yellow (SEQ ID NO:4), adestination vector for use in construction of expression vectors forArabidopsis. The attR1 site is at nucleotides 11276-11399 (complementarystrand); the attR2 site is at nucleotides 9695-9819 (complementarystrand).

FIG. 5 shows a schematic of the vector PHP27840 (SEQ ID NO:5), adestination vector for use in construction of expression vectors forsoybean. The attR1 site is at nucleotides 7310-7434; the attR2 site isat nucleotides 8890-9014.

FIG. 6 shows a schematic of the vector PHP23236 (SEQ ID NO:6), adestination vector for use in construction of expression vectors forGaspe Flint derived maize lines. The attR1 site is at nucleotides2006-2130; the attR2 site is at nucleotides 2899-3023.

FIG. 7 shows a schematic of the vector PHP10523 (SEQ ID NO:7), a plasmidDNA present in Agrobacterium strain LBA4404 (Komari et al., Plant J.10:165-174 (1996); NCBI General Identifier No. 59797027).

FIG. 8 shows a schematic of the vector PHP23235 (SEQ ID NO:8), a vectorused to construct the destination vector PHP23236.

FIG. 9 shows a schematic of the vector PHP20234 (SEQ ID NO:9).

FIG. 10 shows a schematic of the destination vector PHP22655 (SEQ IDNO:10).

FIG. 11 shows a typical grid pattern for five lines (labeled 1 through5-eleven individuals for each line), plus wild-type control C1 (nineindividuals), used in screens.

FIG. 12 shows a graph showing the effect of several different potassiumnitrate concentrations on plant color as determined by image analysis.The response of the green color bin (hues 50 to 66) to nitrate dosagedemonstrates that this bin can be used as an indicator of nitrogenassimilation.

FIG. 13 shows the growth medium used for semi-hydroponics maize growthin Example 18.

FIGS. 14A and 14B show the multiple alignment of the full length aminoacid sequences of the Arabidopsis thaliana LNT2 polypeptide (SEQ IDNO:28) and the LNT2 homologs (SEQ ID NOs: 18, 20, 24, 26, 30, 32, 33,and 34).

FIG. 15 shows a chart of the percent sequence identity and thedivergence values for each pair of amino acids sequences displayed inFIGS. 14A and 14B.

FIGS. 16A-16I shows the results from screening of Gaspe Flint derivedmaize lines under reduced nitrogen (1 mM KNO₃) and optimal nitrogen (6.5mM KNO₃) conditions. Four events containing PHP29689 were evaluated fora number of traits. Event means were compared to that of the segregantnulls. A p-value≦0.1 was used as the cut off.

FIGS. 17A-17C shows the results from screening of Gaspe Flint derivedmaize lines under reduced nitrogen (1 mM KNO₃) and optimal nitrogen (6.5mM KNO₃) conditions. All events containing PHP29689 were considered inthe analysis. For each variable, the construct mean was compared to thatof the construct null. A p-value≦0.1 was used as the cut off.

FIG. 18 shows the yield trial results for PHP28840-containing plantsunder low nitrogen conditions. The yield values in gray representsignificant increases, and the yield values in black representsignificant decreases. The remaining values represent non-significantdifferences.

FIG. 19 shows the yield trial results for PHP28841-containing plantsunder low nitrogen conditions. The yield values in gray representsignificant increases, and the yield values in black representsignificant decreases. The remaining values represent non-significantdifferences.

FIG. 20 shows the yield trial results for PHP28840-containing plantsunder normal nitrogen conditions. The yield values in gray representsignificant increases, and the yield values in black representsignificant decreases. The remaining values represent non-significantdifferences.

FIG. 21 shows the yield trial results for PHP28841-containing plantsunder normal nitrogen conditions. The yield values in gray representsignificant increases, and the yield values in black representsignificant decreases. The remaining values represent non-significantdifferences.

FIG. 22 shows the results of the NUE seedling assay for plantscontaining either PHP28840 (expression cassette=Int2-3) or PHP28841(expression cassette=Int2-2).

The sequence descriptions and Sequence Listing attached hereto complywith the rules governing nucleotide and/or amino acid sequencedisclosures in patent applications as set forth in 37 C.F.R.§1.821-1.825. The Sequence Listing contains the one letter code fornucleotide sequence characters and the three letter codes for aminoacids as defined in conformity with the IUPAC-IUBMB standards describedin Nucleic Acids Res. 13:3021-3030 (1985) and in the Biochemical J. 219(2):345-373 (1984) which are herein incorporated by reference. Thesymbols and format used for nucleotide and amino acid sequence datacomply with the rules set forth in 37 C.F.R. §1.822.

Table 1 lists certain polypeptides that are described herein, thedesignation of the cDNA clones that comprise the nucleic acid fragmentsencoding polypeptides representing all or a substantial portion of thesepolypeptides, and the corresponding identifier (SEQ ID NO:) as used inthe attached Sequence Listing.

TABLE 1 Low Nitrogen tolerant proteins (LNT) SEQ ID NO: Amino CloneDesignation Nucleotide Acid LNT2-like cpg1c.pk013.o6:fis 17 18 LNT2-likerca1n.pk001.f6:fis 19 20 LNT2-like sfl1n1.pk002.j1 21 LNT2-likesds1f.pk001.k5 22

SEQ ID NO:1 is the nucleotide sequence of the pHSbarENDs2 activationtagging vector (FIG. 1).

SEQ ID NO:2 is the nucleotide sequence of the pDONR™Zeo construct (FIG.2).

SEQ ID NO:3 is the nucleotide sequence of the pDONR™221 construct (FIG.3).

SEQ ID NO:4 is the nucleotide sequence of the pBC-yellow vector (FIG.4).

SEQ ID NO:5 is the nucleotide sequence of the PHP27840 vector (FIG. 5).

SEQ ID NO:6 is the nucleotide sequence of the destination vectorPHP23236 (FIG. 6).

SEQ ID NO:7 is the nucleotide sequence of the PHP10523 vector (FIG. 7).

SEQ ID NO:8 is the nucleotide sequence of the PHP23235 vector (FIG. 8).

SEQ ID NO:9 is the nucleotide sequence of the PHP20234 vector (FIG. 9).

SEQ ID NO:10 is the nucleotide sequence of the destination vectorPHP22655 (FIG. 10).

SEQ ID NO:11 is the nucleotide sequence of the poly-linker used tosubstitute the PacI restriction site at position 5775 of pHSbarENDs2.

SEQ ID NO:12 is the nucleotide sequence of the attB1 sequence.

SEQ ID NO:13 is the nucleotide sequence of the attB2 sequence.

SEQ ID NO:14 is the nucleotide sequence of the entry clone PHP23112.

SEQ ID NO:15 is the forward primer VC062 in Example 5.

SEQ ID NO:16 is the reverse primer VC063 in Example 5.

SEQ ID NOs:17-22 (see Table 1).

SEQ ID NO:23 is the consensus nucleotide sequence of a contig, referredto herein as PSO415619, containing B1316280 (NCBI General Identifier No.14990607), CD401485 (NCBI General Identifier No. 31459457) andsfl1n1.pk002.j1 (SEQ ID NO:21).

SEQ ID NO:24 is the amino acid sequence of the polypeptide encoded byPSO415619 (SEQ ID NO:23).

SEQ ID NO:25 is the consensus nucleotide sequence of a contig, referredto herein as PSO415620, containing CX548557 (NCBI General Identifier No.57575582) and sds1f.pk001.k5 (SEQ ID NO:22).

SEQ ID NO:26 is the amino acid sequence of the polypeptide encoded byPSO415620 (SEQ ID NO:25).

SEQ ID NO:27 is the nucleotide sequence of the gene that encodes theArabidopsis thaliana “unknown protein” (LNT2) (At5g50930; NCBI GeneralIdentifier No. 145359102).

SEQ ID NO:28 is the amino acid sequence of the Arabidopsis thaliana“unknown protein” (LNT2) (At5g50930; NCBI General Identifier No.15241317).

SEQ ID NO:29 is the nucleotide sequence of an alternative splice variant(referred to herein as “Int2-2”) of At5g50930.

SEQ ID NO:30 is the amino acid sequence of the polypeptide encoded byInt2-2 (SEQ ID NO:29) and is referred to herein as “LNT2-2”.

SEQ ID NO:31 is the nucleotide sequence of a second alternative splicevariant (referred to herein as “Int2-3”) of At5g50930.

SEQ ID NO:32 is the amino acid sequence of the polypeptide encoded byInt2-3 (SEQ ID NO:29) and is referred to herein as “LNT2-3”. SEQ IDNO:32 is 100% identical to SEQ ID NO:52198 in EP1033405 based on theClustal V method of alignment, using default parameters.

SEQ ID NO:33 is the amino acid sequence of the Oryza sativa “unknownprotein” (NCBI General Identifier No. 38347162).

SEQ ID NO:34 is the amino acid sequence of the Vitis vinifera“hypothetical protein” (NCBI General Identifier No. 147791927).

SEQ ID NO:35 is the nucleotide sequence of the At5g50930-5′ attB forwardprimer.

SEQ ID NO:36 is the nucleotide sequence of the At5g50930-3′ attB reverseprimer.

DETAILED DESCRIPTION OF OTHER EMBODIMENTS

The disclosure of each reference set forth herein is hereby incorporatedby reference in its entirety.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural reference unless the context clearly dictatesotherwise. Thus, for example, reference to “a plant” includes aplurality of such plants, reference to “a cell” includes one or morecells and equivalents thereof known to those skilled in the art, and soforth.

As used herein:

“Nitrogen limiting conditions” refers to conditions where the amount oftotal available nitrogen (e.g., from nitrates, ammonia, or other knownsources of nitrogen) is not sufficient to sustain optimal plant growthand development. One skilled in the art would recognize conditions wheretotal available nitrogen is sufficient to sustain optimal plant growthand development. One skilled in the art would recognize what constitutessufficient amounts of total available nitrogen, and what constitutessoils, media and fertilizer inputs for providing nitrogen to plants.Nitrogen limiting conditions will vary depending upon a number offactors, including but not limited to, the particular plant andenvironmental conditions.

“Agronomic characteristic” is a measurable parameter including but notlimited to, greenness, yield, growth rate, biomass, fresh weight atmaturation, dry weight at maturation, fruit yield, seed yield, totalplant nitrogen content, fruit nitrogen content, seed nitrogen content,nitrogen content in vegetative tissue, whole plant amino acid content,vegetative tissue free amino acid content, fruit free amino acidcontent, seed free amino acid content, total plant protein content,fruit protein content, seed protein content, protein content in avegetative tissue, drought tolerance, nitrogen uptake, resistance toroot lodging, harvest index, stalk lodging, plant height, ear height,and ear length.

“Harvest index” refers to the grain weight divided by the total plantweight.

“Int2” refers to the Arabidopsis thaliana gene locus, At5g50930 (SEQ IDNO: 27). “LNT2” refers to the protein (SEQ ID NO:28) encoded by SEQ IDNO:27.

“Int2-2” (SEQ ID NO:29) and “Int2-3” (SEQ ID NO:31) are naturallyoccurring alternative splice variants of the At5g50930 gene. “LNT2-2”(SEQ ID NO:30) and “LNT2-3” (SEQ ID NO:32) refer to the proteins encodedby “Int2-2” and “Int2-3”, respectively.

“Int2-like” refers to nucleotide homologs from different species, suchas corn and soybean, of the Arabidopsis thaliana “Int2” locus At5g50930(SEQ ID NO: 28) and includes without limitation any of the nucleotidesequences of SEQ ID NOs: 17, 19, 23, and 25.

“LNT2-like” refers to protein homologs from different species, such ascorn and soybean, of the Arabidopsis thaliana “LNT2” (SEQ ID NO: 28) andincludes without limitation any of the amino acid sequences of SEQ IDNOs: 18, 20, 24, and 26.

“Alternative splice variants” used herein refers to alternative forms ofRNA transcribed from a gene. Splice variation naturally occurs as aresult of alternative sites being spliced within a single transcribedRNA molecule or between separately transcribed RNA molecules, and mayresult in several different forms of mRNA transcribed from the samegene. Thus, splice variants may encode polypeptides having differentamino acid sequences, which may or may not have similar functions in theorganism.

“Nitrogen stress tolerance” is a trait of a plant and refers to theability of the plant to survive under nitrogen limiting conditions.

“Increased nitrogen stress tolerance” of a plant is measured relative toa reference or control plant, and means that the nitrogen stresstolerance of the plant is increased by any amount or measure whencompared to the nitrogen stress tolerance of the reference or controlplant.

A “nitrogen stress tolerant plant” is a plant that exhibits nitrogenstress tolerance. A nitrogen stress tolerant plant is In an embodiment aplant that exhibits an increase in at least one agronomic characteristicrelative to a control plant under nitrogen limiting conditions.

“Environmental conditions” refer to conditions under which the plant isgrown, such as the availability of water, availability of nutrients (forexample nitrogen), or the presence of insects or disease.

“Transgenic” refers to any cell, cell line, callus, tissue, plant partor plant, the genome of which has been altered by the presence of aheterologous nucleic acid, such as a recombinant DNA construct,including those initial transgenic events as well as those created bysexual crosses or asexual propagation from the initial transgenic event.The term “transgenic” as used herein does not encompass the alterationof the genome (chromosomal or extra-chromosomal) by conventional plantbreeding methods or by naturally occurring events such as randomcross-fertilization, non-recombinant viral infection, non-recombinantbacterial transformation, non-recombinant transposition, or spontaneousmutation.

“Genome” as it applies to plant cells encompasses not only chromosomalDNA found within the nucleus, but organelle DNA found within subcellularcomponents (e.g., mitochondrial, plastid) of the cell.

“Plant” includes reference to whole plants, plant organs, plant tissues,seeds and plant cells and progeny of same. Plant cells include, withoutlimitation, cells from seeds, suspension cultures, embryos, meristematicregions, callus tissue, leaves, roots, shoots, gametophytes,sporophytes, pollen, and microspores.

“Progeny” comprises any subsequent generation of a plant.

“Transgenic plant” includes reference to a plant which comprises withinits genome a heterologous polynucleotide. In an embodiment, theheterologous polynucleotide is stably integrated within the genome suchthat the polynucleotide is passed on to successive generations. Theheterologous polynucleotide may be integrated into the genome alone oras part of a recombinant DNA construct.

“Heterologous” with respect to sequence means a sequence that originatesfrom a foreign species, or, if from the same species, is substantiallymodified from its native form in composition and/or genomic locus bydeliberate human intervention.

“Polynucleotide”, “nucleic acid sequence”, “nucleotide sequence”, or“nucleic acid fragment” are used interchangeably to refer to a polymerof RNA or DNA that is single- or double-stranded, optionally containingsynthetic, non-natural or altered nucleotide bases. Nucleotides (usuallyfound in their 5′-monophosphate form) are referred to by their singleletter designation as follows: “A” for adenylate or deoxyadenylate (forRNA or DNA, respectively), “C” for cytidylate or deoxycytidylate, “G”for guanylate or deoxyguanylate, “U” for uridylate, “T” fordeoxythymidylate, “R” for purines (A or G), “Y” for pyrimidines (C orT), “K” for G or T, “H” for A or C or T, “I” for inosine, and “N” forany nucleotide.

“Polypeptide”, “peptide”, “amino acid sequence” and “protein” are usedinterchangeably herein to refer to a polymer of amino acid residues. Theterms apply to amino acid polymers in which one or more amino acidresidue is an artificial chemical analogue of a corresponding naturallyoccurring amino acid, as well as to naturally occurring amino acidpolymers. The terms “polypeptide”, “peptide”, “amino acid sequence”, and“protein” are also inclusive of modifications including, but not limitedto, glycosylation, lipid attachment, sulfation, gamma-carboxylation ofglutamic acid residues, hydroxylation and ADP-ribosylation.

“Messenger RNA (mRNA)” refers to the RNA that is without introns andthat can be translated into protein by the cell.

“cDNA” refers to a DNA that is complementary to and synthesized from anmRNA template using the enzyme reverse transcriptase. The cDNA can besingle-stranded or converted into the double-stranded form using theKlenow fragment of DNA polymerase I.

An “Expressed Sequence Tag” (“EST”) is a DNA sequence derived from acDNA library and therefore is a sequence which has been transcribed. AnEST is typically obtained by a single sequencing pass of a cDNA insert.The sequence of an entire cDNA insert is termed the “Full-InsertSequence” (“FIS”). A “Contig” sequence is a sequence assembled from twoor more sequences that can be selected from, but not limited to, thegroup consisting of an EST, FIS and PCR sequence. A sequence encoding anentire or functional protein is termed a “Complete Gene Sequence”(“CGS”) and can be derived from an FIS or a contig.

“Mature” protein refers to a post-translationally processed polypeptide;i.e., one from which any pre- or pro-peptides present in the primarytranslation product have been removed.

“Precursor” protein refers to the primary product of translation ofmRNA; i.e., with pre- and pro-peptides still present. Pre- andpro-peptides may be and are not limited to intracellular localizationsignals.

“Isolated” refers to materials, such as nucleic acid molecules and/orproteins, which are substantially free or otherwise removed fromcomponents that normally accompany or interact with the materials in anaturally occurring environment. Isolated polynucleotides may bepurified from a host cell in which they naturally occur. Conventionalnucleic acid purification methods known to skilled artisans may be usedto obtain isolated polynucleotides. The term also embraces recombinantpolynucleotides and chemically synthesized polynucleotides.

“Recombinant” refers to an artificial combination of two otherwiseseparated segments of sequence, e.g., by chemical synthesis or by themanipulation of isolated segments of nucleic acids by geneticengineering techniques. “Recombinant” also includes reference to a cellor vector, that has been modified by the introduction of a heterologousnucleic acid or a cell derived from a cell so modified, but does notencompass the alteration of the cell or vector by naturally occurringevents (e.g., spontaneous mutation, naturaltransformation/transduction/transposition) such as those occurringwithout deliberate human intervention.

“Recombinant DNA construct” refers to a combination of nucleic acidfragments that are not normally found together in nature. Accordingly, arecombinant DNA construct may comprise regulatory sequences and codingsequences that are derived from different sources, or regulatorysequences and coding sequences derived from the same source, butarranged in a manner different than that normally found in nature.

The terms “entry clone” and “entry vector” are used interchangeablyherein.

“Regulatory sequences” and “regulatory elements” are usedinterchangeably and refer to nucleotide sequences located upstream (5′non-coding sequences), within, or downstream (3′ non-coding sequences)of a coding sequence, and which influence the transcription, RNAprocessing or stability, or translation of the associated codingsequence. Regulatory sequences may include, but are not limited to,promoters, translation leader sequences, introns, and polyadenylationrecognition sequences.

“Promoter” refers to a nucleic acid fragment capable of controllingtranscription of another nucleic acid fragment.

“Promoter functional in a plant” is a promoter capable of controllingtranscription in plant cells whether or not its origin is from a plantcell.

“Tissue-specific promoter” and “tissue-preferred promoter” are usedinterchangeably to refer to a promoter that is expressed predominantlybut not necessarily exclusively in one tissue or organ, but that mayalso be expressed in one specific cell.

“Developmentally regulated promoter” refers to a promoter whose activityis determined by developmental events.

“Operably linked” refers to the association of nucleic acid fragments ina single fragment so that the function of one is regulated by the other.For example, a promoter is operably linked with a nucleic acid fragmentwhen it is capable of regulating the transcription of that nucleic acidfragment.

“Expression” refers to the production of a functional product. Forexample, expression of a nucleic acid fragment may refer totranscription of the nucleic acid fragment (e.g., transcriptionresulting in mRNA or functional RNA) and/or translation of mRNA into aprecursor or mature protein.

“Phenotype” means the detectable characteristics of a cell or organism.

“Introduced” in the context of inserting a nucleic acid fragment (e.g.,a recombinant DNA construct) into a cell, means “transfection” or“transformation” or “transduction” and includes reference to theincorporation of a nucleic acid fragment into a eukaryotic orprokaryotic cell where the nucleic acid fragment may be incorporatedinto the genome of the cell (e.g., chromosome, plasmid, plastid ormitochondrial DNA), converted into an autonomous replicon, ortransiently expressed (e.g., transfected mRNA).

A “transformed cell” is any cell into which a nucleic acid fragment(e.g., a recombinant DNA construct) has been introduced.

“Transformation” as used herein refers to both stable transformation andtransient transformation.

“Stable transformation” refers to the introduction of a nucleic acidfragment into a genome of a host organism resulting in geneticallystable inheritance. Once stably transformed, the nucleic acid fragmentis stably integrated in the genome of the host organism and anysubsequent generation.

“Transient transformation” refers to the introduction of a nucleic acidfragment into the nucleus, or DNA-containing organelle, of a hostorganism resulting in gene expression without genetically stableinheritance.

“Allele” is one of several alternative forms of a gene occupying a givenlocus on a chromosome. When the alleles present at a given locus on apair of homologous chromosomes in a diploid plant are the same thatplant is homozygous at that locus. If the alleles present at a givenlocus on a pair of homologous chromosomes in a diploid plant differ thatplant is heterozygous at that locus. If a transgene is present on one ofa pair of homologous chromosomes in a diploid plant that plant ishemizygous at that locus.

Sequence alignments and percent identity calculations may be determinedusing a variety of comparison methods designed to detect homologoussequences including, but not limited to, the MEGALIGN® program of theLASERGENE® bioinformatics computing suite (DNASTAR® Inc., Madison,Wis.). Unless stated otherwise, multiple alignment of the sequencesprovided herein were performed using the Clustal V method of alignment(Higgins and Sharp, CABIOS. 5:151-153 (1989)) with the defaultparameters (GAP PENALTY=10, GAP LENGTH PENALTY=10). Default parametersfor pairwise alignments and calculation of percent identity of proteinsequences using the Clustal V method are KTUPLE=1, GAP PENALTY=3,WINDOW=5 and DIAGONALS SAVED=5. For nucleic acids these parameters areKTUPLE=2, GAP PENALTY=5, WINDOW=4 and DIAGONALS SAVED=4. After alignmentof the sequences, using the Clustal V program, it is possible to obtain“percent identity” and “divergence” values by viewing the “sequencedistances” table on the same program; unless stated otherwise, percentidentities and divergences provided and claimed herein were calculatedin this manner.

Standard recombinant DNA and molecular cloning techniques used hereinare well known in the art and are described more fully in Sambrook, J.,Fritsch, E. F. and Maniatis, T. Molecular Cloning: A Laboratory Manual;Cold Spring Harbor Laboratory Press: Cold Spring Harbor, 1989(hereinafter “Sambrook”).

Turning now to several embodiments:

Other embodiments include isolated polynucleotides and polypeptides,recombinant DNA constructs, compositions (such as plants or seeds)comprising these recombinant DNA constructs, and methods utilizing theserecombinant DNA constructs.

Other Isolated Polynucleotides and Polypeptides

The present invention includes the following other isolatedpolynucleotides and polypeptides:

An isolated polynucleotide comprising: (i) a nucleic acid sequenceencoding a polypeptide having an amino acid sequence of at least 50%,51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%,65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%,79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based onthe Clustal V method of alignment, when compared to SEQ ID NO:18, 20,24, 26, 28, 30, or 32; or (ii) a full complement of the nucleic acidsequence of (i), wherein the full complement and the nucleic acidsequence of (i) consist of the same number of nucleotides and are 100%complementary. Any of the foregoing isolated polynucleotides may beutilized in any recombinant DNA constructs (including suppression DNAconstructs) of the present invention. The polypeptide can be an LNT2 orLNT2-like protein.

An isolated polypeptide having an amino acid sequence of at least 50%,51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%,65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%,79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based onthe Clustal V method of alignment, when compared to SEQ ID NO:18, 20,24, 26, 28, 30, or 32. The polypeptide is can be an LNT2 or LNT2-likeprotein.

An isolated polynucleotide comprising (i) a nucleic acid sequence of atleast 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%,63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%,77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%,91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity,based on the Clustal V method of alignment, when compared to SEQ IDNO:17, 19, 23, 25, 27, 29, or 31; or (ii) a full complement of thenucleic acid sequence of (i). Any of the foregoing isolatedpolynucleotides may be utilized in any recombinant DNA constructs(including suppression DNA constructs) of the present invention. Theisolated polynucleotide can be encodes an LNT2 or LNT2-like protein.

Other Recombinant DNA Constructs and Suppression DNA Constructs

In one aspect, the present invention includes recombinant DNA constructs(including suppression DNA constructs).

In one other embodiment, a recombinant DNA construct comprises apolynucleotide operably linked to at least one regulatory sequence(e.g., a promoter functional in a plant), wherein the polynucleotidecomprises (i) a nucleic acid sequence encoding an amino acid sequence ofat least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%,62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%,76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%,90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequenceidentity, based on the Clustal V method of alignment, when compared toSEQ ID NO:18, 20, 24, 26, 28, 30, or 32; or (ii) a full complement ofthe nucleic acid sequence of (i).

In another other embodiment, a recombinant DNA construct comprises apolynucleotide operably linked to at least one regulatory sequence(e.g., a promoter functional in a plant), wherein said polynucleotidecomprises (i) a nucleic acid sequence of at least 50%, 51%, 52%, 53%,54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%,68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%,82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO:17, 19, 23, 25, 27, 29,or 31; or (ii) a full complement of the nucleic acid sequence of (i).

FIGS. 14A and 14B show the multiple alignment of the amino acidsequences of SEQ ID NOs: 18, 20, 24, 26, 28, 30, 32, 33, and 34 Themultiple alignment of the sequences was performed using the MEGALIGN®program of the LASERGENE® bioinformatics computing suite (DNASTAR® Inc.,Madison, Wis.); in particular, using the Clustal V method of alignment(Higgins and Sharp, CABIOS. 5:151-153 (1989)) with the multiplealignment default parameters of GAP PENALTY=10 and GAP LENGTHPENALTY=10, and the pairwise alignment default parameters of KTUPLE=1,GAP PENALTY=3, WINDOW=5 and DIAGONALS SAVED=5.

FIG. 15 is a chart of the percent sequence identity and the divergencevalues for each pair of amino acids sequences displayed in FIGS. 14A and14B.

In another other embodiment, a recombinant DNA construct comprises apolynucleotide operably linked to at least one regulatory sequence(e.g., a promoter functional in a plant), wherein said polynucleotideencodes an LNT2 or LNT2-like protein.

In another aspect, the present invention includes suppression DNAconstructs.

A suppression DNA construct can comprise at least one regulatorysequence (in an embodiment a promoter functional in a plant) operablylinked to (a) all or part of: (i) a nucleic acid sequence encoding apolypeptide having an amino acid sequence of at least 50%, 51%, 52%,53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%, 65%, 66%,67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%,81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%,95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based on the ClustalV method of alignment, when compared to SEQ ID NO:18, 20, 24, 26, 28,30, or 32; or (ii) a full complement of the nucleic acid sequence of(a)(i); or (b) a region derived from all or part of a sense strand orantisense strand of a target gene of interest, said region having anucleic acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%,57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%,71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%,85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%,99%, or 100% sequence identity, based on the Clustal V method ofalignment, when compared to said all or part of a sense strand orantisense strand from which said region is derived, and wherein saidtarget gene of interest encodes an LNT2 or LNT2-like protein; or (c) allor part of: (i) a nucleic acid sequence of at least 50%, 51%, 52%, 53%,54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%,68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%,82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99%, or 100% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO:17, 19, 23, 25, 27, 29,or 31; or (ii) a full complement of the nucleic acid sequence of (c)(i).The suppression DNA construct in an embodiment, comprises acosuppression construct, antisense construct, viral-suppressionconstruct, hairpin suppression construct, stem-loop suppressionconstruct, double-stranded RNA-producing construct, RNAi construct, orsmall RNA construct (e.g., an sRNA construct or an miRNA construct).

It is understood, as those skilled in the art will appreciate, that theinvention encompasses more than the specific exemplary sequences.Alterations in a nucleic acid fragment which result in the production ofa chemically equivalent amino acid at a given site, but do not affectthe functional properties of the encoded polypeptide, are well known inthe art. For example, a codon for the amino acid alanine, a hydrophobicamino acid, may be substituted by a codon encoding another lesshydrophobic residue, such as glycine, or a more hydrophobic residue,such as valine, leucine, or isoleucine. Similarly, changes which resultin substitution of one negatively charged residue for another, such asaspartic acid for glutamic acid, or one positively charged residue foranother, such as lysine for arginine, can also be expected to produce afunctionally equivalent product. Nucleotide changes which result inalteration of the N-terminal and C-terminal portions of the polypeptidemolecule would also not be expected to alter the activity of thepolypeptide. Each of the proposed modifications is well within theroutine skill in the art, as is determination of retention of biologicalactivity of the encoded products.

“Suppression DNA construct” is a recombinant DNA construct which whentransformed or stably integrated into the genome of the plant, resultsin “silencing” of a target gene in the plant. The target gene may beendogenous or transgenic to the plant. “Silencing,” as used herein withrespect to the target gene, refers generally to the suppression oflevels of mRNA or protein/enzyme expressed by the target gene, and/orthe level of the enzyme activity or protein functionality. The terms“suppression”, “suppressing” and “silencing”, used interchangeablyherein, includes lowering, reducing, declining, decreasing, inhibiting,eliminating or preventing. “Silencing” or “gene silencing” does notspecify mechanism and is inclusive, and not limited to, anti-sense,cosuppression, viral-suppression, hairpin suppression, stem-loopsuppression, RNAi-based approaches, and small RNA-based approaches.

A suppression DNA construct may comprise a region derived from a targetgene of interest and may comprise all or part of the nucleic acidsequence of the sense strand (or antisense strand) of the target gene ofinterest. Depending upon the approach to be utilized, the region may be100% identical or less than 100% identical (e.g., at least 50%, 51%,52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%, 65%,66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%,80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, or 99% identical) to all or part of the sensestrand (or antisense strand) of the gene of interest.

Suppression DNA constructs are well-known in the art, are readilyconstructed once the target gene of interest is selected, and include,without limitation, cosuppression constructs, antisense constructs,viral-suppression constructs, hairpin suppression constructs, stem-loopsuppression constructs, double-stranded RNA-producing constructs, andmore generally, RNAi (RNA interference) constructs and small RNAconstructs such as sRNA (short interfering RNA) constructs and miRNA(microRNA) constructs.

“Antisense inhibition” refers to the production of antisense RNAtranscripts capable of suppressing the expression of the target gene orgene product. “Antisense RNA” refers to an RNA transcript that iscomplementary to all or part of a target primary transcript or mRNA andthat blocks the expression of a target isolated nucleic acid fragment(U.S. Pat. No. 5,107,065). The complementarity of an antisense RNA maybe with any part of the specific gene transcript, i.e., at the 5′non-coding sequence, 3′ non-coding sequence, introns, or the codingsequence.

“Cosuppression” refers to the production of sense RNA transcriptscapable of suppressing the expression of the target gene or geneproduct. “Sense” RNA refers to RNA transcript that includes the mRNA andcan be translated into protein within a cell or in vitro. Cosuppressionconstructs in plants have been previously designed by focusing onoverexpression of a nucleic acid sequence having homology to a nativemRNA, in the sense orientation, which results in the reduction of allRNA having homology to the overexpressed sequence (see Vaucheret et al.,Plant J. 16:651-659 (1998); and Gura, Nature 404:804-808 (2000)).

Another variation describes the use of plant viral sequences to directthe suppression of proximal mRNA encoding sequences (PCT Publication No.WO 98/36083 published on Aug. 20, 1998).

Previously described is the use of “hairpin” structures that incorporateall, or part, of an mRNA encoding sequence in a complementaryorientation that results in a potential “stem-loop” structure for theexpressed RNA (PCT Publication No. WO 99/53050 published on Oct. 21,1999). In this case the stem is formed by polynucleotides correspondingto the gene of interest inserted in either sense or anti-senseorientation with respect to the promoter and the loop is formed by somepolynucleotides of the gene of interest, which do not have a complementin the construct. This increases the frequency of cosuppression orsilencing in the recovered transgenic plants. For a review of hairpinsuppression see Wesley, S. V. et al. (2003) Methods in MolecularBiology, Plant Functional Genomics: Methods and Protocols 236:273-286.

A construct where the stem is formed by at least 30 nucleotides from agene to be suppressed and the loop is formed by a random nucleotidesequence has also effectively been used for suppression (PCT PublicationNo. WO 99/61632 published on Dec. 2, 1999).

The use of poly-T and poly-A sequences to generate the stem in thestem-loop structure has also been described (PCT Publication No. WO02/00894 published Jan. 3, 2002).

Yet another variation includes using synthetic repeats to promoteformation of a stem in the stem-loop structure. Transgenic organismsprepared with such recombinant DNA fragments have been shown to havereduced levels of the protein encoded by the nucleotide fragment formingthe loop as described in PCT Publication No. WO 02/00904, published Jan.3, 2002.

RNA interference refers to the process of sequence-specificpost-transcriptional gene silencing in animals mediated by shortinterfering RNAs (siRNAs) (Fire et al., Nature 391:806 (1998)). Thecorresponding process in plants is commonly referred to aspost-transcriptional gene silencing (PTGS) or RNA silencing and is alsoreferred to as quelling in fungi. The process of post-transcriptionalgene silencing is thought to be an evolutionarily-conserved cellulardefense mechanism used to prevent the expression of foreign genes and iscommonly shared by diverse flora and phyla (Fire et al., Trends Genet.15:358 (1999)). Such protection from foreign gene expression may haveevolved in response to the production of double-stranded RNAs (dsRNAs)derived from viral infection or from the random integration oftransposon elements into a host genome via a cellular response thatspecifically destroys homologous single-stranded RNA of viral genomicRNA. The presence of dsRNA in cells triggers the RNAi response through amechanism that has yet to be fully characterized.

The presence of long dsRNAs in cells stimulates the activity of aribonuclease III enzyme referred to as dicer. Dicer is involved in theprocessing of the dsRNA into short pieces of dsRNA known as shortinterfering RNAs (siRNAs) (Berstein et al., Nature 409:363 (2001)).Short interfering RNAs derived from dicer activity are typically about21 to about 23 nucleotides in length and comprise about 19 base pairduplexes (Elbashir et al., Genes Dev. 15:188 (2001)). Dicer has alsobeen implicated in the excision of 21- and 22-nucleotide small temporalRNAs (stRNAs) from precursor RNA of conserved structure that areimplicated in translational control (Hutvagner et al., Science 293:834(2001)). The RNAi response also features an endonuclease complex,commonly referred to as an RNA-induced silencing complex (RISC), whichmediates cleavage of single-stranded RNA having sequence complementarityto the antisense strand of the siRNA duplex. Cleavage of the target RNAtakes place in the middle of the region complementary to the antisensestrand of the sRNA duplex. In addition, RNA interference can alsoinvolve small RNA (e.g., miRNA) mediated gene silencing, presumablythrough cellular mechanisms that regulate chromatin structure andthereby prevent transcription of target gene sequences (see, e.g.,Allshire, Science 297:1818-1819 (2002); Volpe et al., Science297:1833-1837 (2002); Jenuwein, Science 297:2215-2218 (2002); and Hallet al., Science 297:2232-2237 (2002)). As such, miRNA molecules of theinvention can be used to mediate gene silencing via interaction with RNAtranscripts or alternately by interaction with particular genesequences, wherein such interaction results in gene silencing either atthe transcriptional or post-transcriptional level.

RNAi has been studied in a variety of systems. Fire et al. (Nature391:806 (1998)) were the first to observe RNAi in Caenorhabditiselegans. Wianny and Goetz (Nature Cell Biol. 2:70 (1999)) describe RNAimediated by dsRNA in mouse embryos. Hammond et al. (Nature 404:293(2000)) describe RNAi in Drosophila cells transfected with dsRNA.Elbashir et al., (Nature 411:494 (2001)) describe RNAi induced byintroduction of duplexes of synthetic 21-nucleotide RNAs in culturedmammalian cells including human embryonic kidney and HeLa cells.

Small RNAs play an important role in controlling gene expression.Regulation of many developmental processes, including flowering, iscontrolled by small RNAs. It is now possible to engineer changes in geneexpression of plant genes by using transgenic constructs which producesmall RNAs in the plant.

Small RNAs appear to function by base-pairing to complementary RNA orDNA target sequences. When bound to RNA, small RNAs trigger either RNAcleavage or translational inhibition of the target sequence. When boundto DNA target sequences, it is thought that small RNAs can mediate DNAmethylation of the target sequence. The consequence of these events,regardless of the specific mechanism, is that gene expression isinhibited.

It is thought that sequence complementarity between small RNAs and theirRNA targets helps to determine which mechanism, RNA cleavage ortranslational inhibition, is employed. It is believed that siRNAs whichare perfectly complementary with their targets, work by RNA cleavage.Some miRNAs have perfect or near-perfect complementarity with theirtargets, and RNA cleavage has been demonstrated for at least a few ofthese miRNAs. Other miRNAs have several mismatches with their targets,and apparently inhibit their targets at the translational level. Again,without being held to a particular theory on the mechanism of action, ageneral rule is emerging that perfect or near-perfect complementaritycauses RNA cleavage, whereas translational inhibition is favored whenthe miRNA/target duplex contains many mismatches. The apparent exceptionto this is microRNA 172 (miR172) in plants. One of the targets of miR172is APETALA2 (AP2), and although miR172 shares near-perfectcomplementarity with AP2 it appears to cause translational inhibition ofAP2 rather than RNA cleavage.

MicroRNAs (miRNAs) are noncoding RNAs of about 19 to about 24nucleotides (nt) in length that have been identified in both animals andplants (Lagos-Quintana et al., Science 294:853-858 (2001),Lagos-Quintana et al., Curr. Biol. 12:735-739 (2002); Lau et al.,Science 294:858-862 (2001); Lee and Ambros, Science 294:862-864 (2001);Llave et al., Plant Cell 14:1605-1619 (2002); Mourelatos et al., Genes.Dev. 16:720-728 (2002); Park et al., Curr. Biol. 12:1484-1495 (2002);Reinhart et al., Genes. Dev. 16:1616-1626 (2002)). They are processedfrom longer precursor transcripts that range in size from approximately70 to 200 nt, and these precursor transcripts have the ability to formstable hairpin structures. In animals, the enzyme involved in processingmiRNA precursors is called dicer, an RNAse III-like protein (Grishok etal., Cell 106:23-34 (2001); Hutvagner et al., Science 293:834-838(2001); Ketting et al., Genes. Dev. 15:2654-2659 (2001)). Plants alsohave a dicer-like enzyme, DCL1 (previously named CARPEL FACTORY/SHORTINTEGUMENTS1/SUSPENSOR1), and recent evidence indicates that it, likedicer, is involved in processing the hairpin precursors to generatemature miRNAs (Park et al., Curr. Biol. 12:1484-1495 (2002); Reinhart etal., Genes Dev. 16:1616-1626 (2002)). Furthermore, it is becoming clearfrom recent work that at least some miRNA hairpin precursors originateas longer polyadenylated transcripts, and several different miRNAs andassociated hairpins can be present in a single transcript(Lagos-Quintana et al., Science 294:853-858 (2001); Lee et al., EMBO J.21:4663-4670 (2002)). Recent work has also examined the selection of themiRNA strand from the dsRNA product arising from processing of thehairpin by DICER (Schwartz et al., Cell 115:199-208 (2003)). It appearsthat the stability (i.e., G:C versus A:U content, and/or mismatches) ofthe two ends of the processed dsRNA affects the strand selection, withthe low stability end being easier to unwind by a helicase activity. The5′ end strand at the low stability end is incorporated into the RISCcomplex, while the other strand is degraded.

MicroRNAs (miRNAs) appear to regulate target genes by binding tocomplementary sequences located in the transcripts produced by thesegenes. In the case of lin-4 and let-7, the target sites are located inthe 3′ UTRs of the target mRNAs (Lee et al., Cell 75:843-854 (1993);Wightman et al., Cell 75:855-862 (1993); Reinhart et al., Nature403:901-906 (2000); Slack et al., Mol. Cell 5:659-669 (2000)), and thereare several mismatches between the lin-4 and let-7 miRNAs and theirtarget sites. Binding of the lin-4 or let-7 miRNA appears to causedownregulation of steady-state levels of the protein encoded by thetarget mRNA without affecting the transcript itself (Olsen and Ambros,Dev. Biol. 216:671-680 (1999)). On the other hand, recent evidencesuggests that miRNAs can in some cases cause specific RNA cleavage ofthe target transcript within the target site, and this cleavage stepappears to require 100% complementarity between the miRNA and the targettranscript (Hutvagner and Zamore, Science 297:2056-2060 (2002); Llave etal., Plant Cell 14:1605-1619 (2002)). It seems likely that miRNAs canenter at least two pathways of target gene regulation: (1) proteindownregulation when target complementarity is <100%; and (2) RNAcleavage when target complementarity is 100%. MicroRNAs entering the RNAcleavage pathway are analogous to the 21-25 nt short interfering RNAs(siRNAs) generated during RNA interference (RNAi) in animals andposttranscriptional gene silencing (PTGS) in plants, and likely areincorporated into an RNA-induced silencing complex (RISC) that issimilar or identical to that seen for RNAi.

Identifying the targets of miRNAs with bioinformatics has not beensuccessful in animals, and this is probably due to the fact that animalmiRNAs have a low degree of complementarity with their targets. On theother hand, bioinformatic approaches have been successfully used topredict targets for plant miRNAs (Llave et al., Plant Cell 14:1605-1619(2002); Park et al., Curr. Biol. 12:1484-1495 (2002); Rhoades et al.,Cell 110:513-520 (2002)), and thus it appears that plant miRNAs havehigher overall complementarity with their putative targets than doanimal miRNAs. Most of these predicted target transcripts of plantmiRNAs encode members of transcription factor families implicated inplant developmental patterning or cell differentiation.

Regulatory Sequences:

A recombinant DNA construct (including a suppression DNA construct) ofthe present invention can comprise at least one regulatory sequence.

A regulatory sequence is a promoter.

A number of promoters can be used in recombinant DNA constructs (andsuppression DNA constructs) of the present invention. The promoters canbe selected based on the desired outcome, and may include constitutive,tissue-specific, inducible, or other promoters for expression in thehost organism.

High level, constitutive expression of the candidate gene under controlof the 35S or UBI promoter may (or may not) have pleiotropic effects,although candidate gene efficacy may be estimated when driven by aconstitutive promoter. Use of tissue-specific and/or stress-specificpromoters may eliminate undesirable effects, but retain the ability toenhance nitrogen tolerance. This type of effect has been observed inArabidopsis for drought and cold tolerance (Kasuga et al., NatureBiotechnol. 17:287-91 (1999)).

Suitable constitutive promoters for use in a plant host cell include,for example, the core promoter of the Rsyn7 promoter and otherconstitutive promoters disclosed in WO 99/43838 and U.S. Pat. No.6,072,050; the core CaMV 35S promoter (Odell et al., Nature 313:810-812(1985)); rice actin (McElroy et al., Plant Cell 2:163-171 (1990));ubiquitin (Christensen et al., Plant Mol. Biol. 12:619-632 (1989) andChristensen et al., Plant Mol. Biol. 18:675-689 (1992)); pEMU (Last etal., Theor. Appl. Genet. 81:581-588 (1991)); MAS (Velten et al., EMBO J.3:2723-2730 (1984)); ALS promoter (U.S. Pat. No. 5,659,026), and thelike. Other constitutive promoters include, for example, those discussedin U.S. Pat. Nos. 5,608,149; 5,608,144; 5,604,121; 5,569,597; 5,466,785;5,399,680; 5,268,463; 5,608,142; and 6,177,611.

In choosing a promoter to use in the methods of the invention, it may bedesirable to use a tissue-specific or developmentally regulatedpromoter.

Another tissue-specific or developmentally regulated promoter is a DNAsequence which regulates the expression of a DNA sequence selectively inthe cells/tissues of a plant critical to tassel development, seed set,or both, and limits the expression of such a DNA sequence to the periodof tassel development or seed maturation in the plant. Any identifiablepromoter may be used in the methods of the present invention whichcauses the desired temporal and spatial expression.

Promoters which are seed or embryo-specific and may be useful in theinvention include soybean Kunitz trypsin inhibitor (Kti3, Jofuku andGoldberg, Plant Cell 1:1079-1093 (1989)), patatin (potato tubers)(Rocha-Sosa, M., et al., EMBO J. 8:23-29 (1989)), convicilin, vicilin,and legumin (pea cotyledons) (Rerie, W. G., et al., Mol. Gen. Genet.259:149-157 (1991); Newbigin, E. J., et al., Planta 180:461-470 (1990);Higgins, T. J. V., et al., Plant. Mol. Biol. 11:683-695 (1988)), zein(maize endosperm) (Schemthaner, J. P., et al., EMBO J. 7:1249-1255(1988)), phaseolin (bean cotyledon) (Segupta-Gopalan, C., et al., Proc.Natl. Acad. Sci. U.S.A. 82:3320-3324 (1995)), phytohemagglutinin (beancotyledon) (Voelker, T. et al., EMBO J. 6:3571-3577 (1987)),B-conglycinin and glycinin (soybean cotyledon) (Chen, Z-L, et al., EMBOJ. 7:297-302 (1988)), glutelin (rice endosperm), hordein (barleyendosperm) (Marris, C., et al., Plant Mol. Biol. 10:359-366 (1988)),glutenin and gliadin (wheat endosperm) (Colot, V., et al., EMBO J.6:3559-3564 (1987)), and sporamin (sweet potato tuberous root) (Hattori,T., et al., Plant Mol. Biol. 14:595-604 (1990)). Promoters ofseed-specific genes operably linked to heterologous coding regions inchimeric gene constructions maintain their temporal and spatialexpression pattern in transgenic plants. Such examples includeArabidopsis thaliana 2S seed storage protein gene promoter to expressenkephalin peptides in Arabidopsis and Brassica napus seeds(Vanderkerckhove et al., Bio/Technology 7:L929-932 (1989)), bean lectinand bean beta-phaseolin promoters to express luciferase (Riggs et al.,Plant Sci. 63:47-57 (1989)), and wheat glutenin promoters to expresschloramphenicol acetyl transferase (Colot et al., EMBO J. 6:3559-3564(1987)).

Inducible promoters selectively express an operably linked DNA sequencein response to the presence of an endogenous or exogenous stimulus, forexample by chemical compounds (chemical inducers) or in response toenvironmental, hormonal, chemical, and/or developmental signals.Inducible or regulated promoters include, for example, promotersregulated by light, heat, stress, flooding or drought, phytohormones,wounding, or chemicals such as ethanol, jasmonate, salicylic acid, orsafeners.

Other promoters include the following: 1) the stress-inducible RD29Apromoter (Kasuga et al., Nature Biotechnol. 17:287-91 (1999)); 2) thebarley promoter, B22E; expression of B22E is specific to the pedicel indeveloping maize kernels (“Primary Structure of a Novel Barley GeneDifferentially Expressed in Immature Aleurone Layers”, Klemsdal et al.,Mol. Gen. Genet. 228(1/2):9-16 (1991)); and 3) maize promoter, Zag2(“Identification and molecular characterization of ZAG1, the maizehomolog of the Arabidopsis floral homeotic gene AGAMOUS”, Schmidt etal., Plant Cell 5(7):729-737 (1993); “Structural characterization,chromosomal localization and phylogenetic evaluation of two pairs ofAGAMOUS-like MADS-box genes from maize”, Theissen et al., Gene156(2):155-166 (1995); NCBI GenBank Accession No. X80206)). Zag2transcripts can be detected five days prior to pollination to seven toeight days after pollination (“DAP”), and directs expression in thecarpel of developing female inflorescences and Ciml which is specific tothe nucleus of developing maize kernels. Ciml transcript is detectedfour to five days before pollination to six to eight DAP. Other usefulpromoters include any promoter which can be derived from a gene whoseexpression is maternally associated with developing female florets.

Additional other promoters for regulating the expression of thenucleotide sequences of the present invention in plants arestalk-specific promoters. Such stalk-specific promoters include thealfalfa S2A promoter (GenBank Accession No. EF030816; Abrahams et al.,Plant Mol. Biol. 27:513-528 (1995)) and S2B promoter (GenBank AccessionNo. EF030817) and the like, herein incorporated by reference.

Promoters may be derived in their entirety from a native gene, or becomposed of different elements derived from different promoters found innature, or even comprise synthetic DNA segments. It is understood bythose skilled in the art that different promoters may direct theexpression of a gene in different tissues or cell types, or at differentstages of development, or in response to different environmentalconditions. It is further recognized that since in most cases the exactboundaries of regulatory sequences have not been completely defined, DNAfragments of some variation may have identical promoter activity.Promoters that cause a gene to be expressed in most cell types at mosttimes are commonly referred to as “constitutive promoters”. Newpromoters of various types useful in plant cells are constantly beingdiscovered; numerous examples may be found in the compilation byOkamuro, J. K., and Goldberg, R. B., Biochem. Plants 15:1-82 (1989).

Other promoters may include: RIP2, mLIP15, ZmCOR1, Rab17, CaMV 35S,RD29A, B22E, Zag2, SAM synthetase, ubiquitin, CaMV 19S, nos, Adh,sucrose synthase, R-allele, the vascular tissue other promoters S2A(Genbank accession number EF030816) and S2B (GenBank Accession No.EF030817), and the constitutive promoter GOS2 from Zea mays. Otherpromoters include root promoters, such as the maize NAS2 promoter, themaize Cyclo promoter (US Publication No. 2006/0156439, published Jul.13, 2006), the maize ROOTMET2 promoter (WO 2005/063998, published Jul.14, 2005), the CR1BIO promoter (WO 2006/055487, published May 26, 2006),the CRWAQ81 (WO 2005/035770, published Apr. 21, 2005) and the maizeZRP2.47 promoter (NCBI Accession No. U38790; NCBI GI No. 1063664).

Recombinant DNA constructs (and suppression DNA constructs) of thepresent invention may also include other regulatory sequences including,but not limited to, translation leader sequences, introns, andpolyadenylation recognition sequences. In another other embodiment ofthe present invention, a recombinant DNA construct of the presentinvention further comprises an enhancer or silencer.

An intron sequence can be added to the 5′ untranslated region, theprotein-coding region or the 3′ untranslated region to increase theamount of the mature message that accumulates in the cytosol. Inclusionof a spliceable intron in the transcription unit in both plant andanimal expression constructs has been shown to increase gene expressionat both the mRNA and protein levels up to 1000-fold (Buchman and Berg,Mol. Cell. Biol. 8:4395-4405 (1988); Callis et al., Genes Dev.1:1183-1200 (1987)). Such intron enhancement of gene expression istypically greatest when placed near the 5′ end of the transcriptionunit. Use of maize introns Adh1-S intron 1, 2, and 6, the Bronze-1intron are known in the art. See generally, The Maize Handbook, Chapter116, Freeling and Walbot, Eds., Springer, New York (1994).

If polypeptide expression is desired, it is generally desirable toinclude a polyadenylation region at the 3′-end of a polynucleotidecoding region. The polyadenylation region can be derived from thenatural gene, from a variety of other plant genes, or from T-DNA. The3′-end sequence to be added can be derived from, for example, thenopaline synthase or octopine synthase genes, or alternatively fromanother plant gene, or less in an embodiment from any other eukaryoticgene.

A translation leader sequence is a DNA sequence located between thepromoter sequence of a gene and the coding sequence. The translationleader sequence is present in the fully processed mRNA upstream of thetranslation start sequence. The translation leader sequence may affectprocessing of the primary transcript to mRNA, mRNA stability ortranslation efficiency. Examples of translation leader sequences havebeen described (Turner, R. and Foster, G. D., Mol. Biotech. 3:225(1995)).

Any plant can be selected for the identification of regulatory sequencesand genes to be used in recombinant DNA constructs of the presentinvention. Examples of suitable plant targets for the isolation of genesand regulatory sequences would include but are not limited to alfalfa,apple, apricot, Arabidopsis, artichoke, arugula, asparagus, avocado,banana, barley, beans, beet, blackberry, blueberry, broccoli, brusselssprouts, cabbage, canola, cantaloupe, carrot, cassaya, castorbean,cauliflower, celery, cherry, chicory, cilantro, citrus, clementines,clover, coconut, coffee, corn, cotton, cranberry, cucumber, Douglas fir,eggplant, endive, escarole, eucalyptus, fennel, figs, garlic, gourd,grape, grapefruit, honey dew, jicama, kiwifruit, lettuce, leeks, lemon,lime, Loblolly pine, linseed, maize, mango, melon, mushroom, nectarine,nut, oat, oil palm, oil seed rape, okra, olive, onion, orange, anornamental plant, palm, papaya, parsley, parsnip, pea, peach, peanut,pear, pepper, persimmon, pine, pineapple, plantain, plum, pomegranate,poplar, potato, pumpkin, quince, radiata pine, radicchio, radish,rapeseed, raspberry, rice, rye, sorghum, Southern pine, soybean,spinach, squash, strawberry, sugarbeet, sugarcane, sunflower, sweetpotato, sweetgum, tangerine, tea, tobacco, tomato, triticale, turf,turnip, a vine, watermelon, wheat, yams, and zucchini. Particularlyother plants for the identification of regulatory sequences areArabidopsis, maize, wheat, soybean, and cotton.

Other Compositions

A other composition of the present invention is a plant comprising inits genome any of the recombinant DNA constructs (including any of thesuppression DNA constructs) of the present invention (such as any of theother constructs discussed above). Other compositions also include anyprogeny of the plant, and any seed obtained from the plant or itsprogeny, wherein the progeny or seed comprises within its genome therecombinant DNA construct (or suppression DNA construct). Progenyincludes subsequent generations obtained by self-pollination orout-crossing of a plant. Progeny also includes hybrids and inbreds.

In an embodiment, in hybrid seed propagated crops, mature transgenicplants can be self-pollinated to produce a homozygous inbred plant. Theinbred plant produces seed containing the newly introduced recombinantDNA construct (or suppression DNA construct). These seeds can be grownto produce plants that would exhibit an altered agronomic characteristic(e.g., an increased agronomic characteristic, e.g. under nitrogenlimiting conditions), or used in a breeding program to produce hybridseed, which can be grown to produce plants that would exhibit such analtered agronomic characteristic. In an embodiment, the seeds are maize.

In an embodiment, the plant is a monocotyledonous or dicotyledonousplant, a maize or soybean plant, a maize plant, such as a maize hybridplant or a maize inbred plant. The plant may also be sunflower, sorghum,canola, wheat, alfalfa, cotton, rice, barley or millet.

In an embodiment, the recombinant DNA construct is stably integratedinto the genome of the plant.

Particularly other embodiments include but are not limited to thefollowing other embodiments 1-8:

1. A plant (in an embodiment a maize or soybean plant) comprising in itsgenome a recombinant DNA construct comprising a polynucleotide operablylinked to at least one regulatory sequence, wherein said polynucleotideencodes a polypeptide having an amino acid sequence of at least 50%,51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%,65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%,79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based onthe Clustal V method of alignment, when compared to SEQ ID NO:18, 20,24, 26, 28, 30, or 32, and wherein said plant exhibits increasednitrogen stress tolerance when compared to a control plant notcomprising said recombinant DNA construct. In an embodiment, the plantfurther exhibits an alteration of at least one agronomic characteristicwhen compared to the control plant.

2. A plant (in an embodiment a maize or soybean plant) comprising in itsgenome a recombinant DNA construct comprising:

(a) a polynucleotide operably linked to at least one regulatory element,wherein said polynucleotide encodes a polypeptide having an amino acidsequence of at least 50% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO:18, 20, 24, 26, 28, 30,or 32; or

(b) a suppression DNA construct comprising at least one regulatoryelement operably linked to:

-   -   (i) all or part of: (A) a nucleic acid sequence encoding a        polypeptide having an amino acid sequence of at least 50%        sequence identity, based on the Clustal V method of alignment,        when compared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32, or (B)        a full complement of the nucleic acid sequence of (b)(i)(A); or    -   (ii) a region derived from all or part of a sense strand or        antisense strand of a target gene of interest, said region        having a nucleic acid sequence of at least 50% sequence        identity, based on the Clustal V method of alignment, when        compared to said all or part of a sense strand or antisense        strand from which said region is derived, and wherein said        target gene of interest encodes an LNT2 or LNT2-like        polypeptide,

and wherein said plant exhibits an alteration of at least one agronomiccharacteristic when compared to a control plant not comprising saidrecombinant DNA construct.

3. A plant (in an embodiment a maize or soybean plant) comprising in itsgenome a recombinant DNA construct comprising a polynucleotide operablylinked to at least one regulatory sequence, wherein said polynucleotideencodes an LNT2 or LNT2-like polypeptide, and wherein said plantexhibits increased nitrogen stress tolerance when compared to a controlplant not comprising said recombinant DNA construct. In an embodiment,the plant further exhibits an alteration of at least one agronomiccharacteristic when compared to the control plant. In an embodiment, theLNT2 polypeptide is from Arabidopsis thaliana, Zea mays, Glycine max,Glycine tabacina, Glycine soja or Glycine tomentella.

4. A plant (in an embodiment a maize or soybean plant) comprising in itsgenome a recombinant DNA construct comprising a polynucleotide operablylinked to at least one regulatory sequence, wherein said polynucleotideencodes an LNT2 or LNT2-like polypeptide, and wherein said plantexhibits an alteration of at least one agronomic characteristic undernitrogen limiting conditions when compared to a control plant notcomprising said recombinant DNA construct. In an embodiment, the LNT2polypeptide is from Arabidopsis thaliana, Zea mays, Glycine max, Glycinetabacina, Glycine soja or Glycine tomentella.

5. A plant (in an embodiment a maize or soybean plant) comprising in itsgenome a recombinant DNA construct comprising a polynucleotide operablylinked to at least one regulatory element, wherein said polynucleotideencodes a polypeptide having an amino acid sequence of at least 50%,51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%,65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%,79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based onthe Clustal V method of alignment, when compared to SEQ ID NO:18, 20,24, 26, 28, 30, or 32, and wherein said plant exhibits an alteration ofat least one agronomic characteristic under nitrogen limiting conditionswhen compared to a control plant not comprising said recombinant DNAconstruct.

6. A plant (in an embodiment a maize or soybean plant) comprising in itsgenome a suppression DNA construct comprising at least one regulatoryelement operably linked to a region derived from all or part of a sensestrand or antisense strand of a target gene of interest, said regionhaving a nucleic acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%,56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%,70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%,84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%,98%, 99%, or 100% sequence identity, based on the Clustal V method ofalignment, when compared to said all or part of a sense strand orantisense strand from which said region is derived, and wherein saidtarget gene of interest encodes an LNT2 or LNT2-like polypeptide, andwherein said plant exhibits an alteration of at least one agronomiccharacteristic under nitrogen limiting conditions when compared to acontrol plant not comprising said suppression DNA construct.

7. A plant (in an embodiment a maize or soybean plant) comprising in itsgenome a suppression DNA construct comprising at least one regulatoryelement operably linked to all or part of: (a) a nucleic acid sequenceencoding a polypeptide having an amino acid sequence of at least 50%,51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%,65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%,79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based onthe Clustal V method of alignment, when compared to SEQ ID NO:18, 20,24, 26, 28, 30, or 32; or (b) a full complement of the nucleic acidsequence of (a), and wherein said plant exhibits an alteration of atleast one agronomic characteristic under nitrogen limiting conditionswhen compared to a control plant not comprising said suppression DNAconstruct.

8. Any progeny of the above plants in other embodiments 1-7, any seedsof the above plants in other embodiments 1-7, any seeds of progeny ofthe above plants in other embodiments 1-7, and cells from any of theabove plants in other embodiments 1-7 and progeny thereof.

In any of the foregoing other embodiments 1-8 or any other embodimentsof the present invention, the recombinant DNA construct (or suppressionDNA construct) In an embodiment comprises at least a promoter functionalin a plant as a other regulatory sequence.

In any of the foregoing other embodiments 1-8 or any other embodimentsof the present invention, the alteration of at least one agronomiccharacteristic is either an increase or decrease, In an embodiment anincrease.

In any of the foregoing other embodiments 1-8 or any other embodimentsof the present invention, the at least one agronomic characteristicselected from the group consisting of greenness, yield, growth rate,biomass, fresh weight at maturation, dry weight at maturation, fruityield, seed yield, total plant nitrogen content, fruit nitrogen content,seed nitrogen content, nitrogen content in a vegetative tissue, wholeplant amino acid content, vegetative tissue free amino acid content,fruit free amino acid content, seed free amino acid content, total plantprotein content, fruit protein content, seed protein content, proteincontent in a vegetative tissue, drought tolerance, nitrogen uptake,resistance to root lodging, harvest index, stalk lodging, plant height,ear height, and ear length. Yield, greenness and biomass areparticularly other agronomic characteristics for alteration (In anembodiment an increase).

In any of the foregoing other embodiments 1-8 or any other embodimentsof the present invention, the plant In an embodiment exhibits thealteration of at least one agronomic characteristic when compared, undernitrogen stress conditions, to a control plant not comprising saidrecombinant DNA construct (or suppression DNA construct).

One of ordinary skill in the art is familiar with protocols forsimulating nitrogen conditions, whether limiting or non-limiting, andfor evaluating plants that have been subjected to simulated ornaturally-occurring nitrogen conditions, whether limiting ornon-limiting. For example, one can simulate nitrogen conditions bygiving plants less nitrogen than normally required or no nitrogen over aperiod of time, and one can evaluate such plants by looking fordifferences in agronomic characteristics, e.g., changes in physiologicaland/or physical condition, including (but not limited to) vigor, growth,size, or root length, or in particular, leaf color or leaf area size.Other techniques for evaluating such plants include measuringchlorophyll fluorescence, photosynthetic rates, root growth or gasexchange rates.

The Examples below describe some representative protocols and techniquesfor simulating nitrogen limiting conditions and/or evaluating plantsunder such conditions.

One can also evaluate nitrogen stress tolerance by the ability of aplant to maintain sufficient yield (In an embodiment at least 75%, 76%,77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%,91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% yield) in fieldtesting under simulated or naturally-occurring low or high nitrogenconditions (e.g., by measuring for substantially equivalent yield underlow or high nitrogen conditions compared to normal nitrogen conditions,or by measuring for less yield loss under low or high nitrogenconditions compared to a control or reference plant).

One of ordinary skill in the art would readily recognize a suitablecontrol or reference plant to be utilized when assessing or measuring anagronomic characteristic or phenotype of a transgenic plant in anyembodiment of the present invention in which a control or preferenceplant is utilized (e.g., compositions or methods as described herein).For example, by way of non-limiting illustrations:

1. Progeny of a transformed plant which is hemizygous with respect to arecombinant DNA construct (or suppression DNA construct), such that theprogeny are segregating into plants either comprising or not comprisingthe recombinant DNA construct (or suppression DNA construct): theprogeny comprising the recombinant DNA construct (or suppression DNAconstruct) would be typically measured relative to the progeny notcomprising the recombinant DNA construct (or suppression DNA construct)(i.e., the progeny not comprising the recombinant DNA construct (or thesuppression DNA construct) is the control or reference plant).

2. Introgression of a recombinant DNA construct (or suppression DNAconstruct) into an inbred line, such as in maize, or into a variety,such as in soybean: the introgressed line would typically be measuredrelative to the parent inbred or variety line (i.e., the parent inbredor variety line is the control or reference plant).

3. Two hybrid lines, where the first hybrid line is produced from twoparent inbred lines, and the second hybrid line is produced from thesame two parent inbred lines except that one of the parent inbred linescontains a recombinant DNA construct (or suppression DNA construct): thesecond hybrid line would typically be measured relative to the firsthybrid line (i.e., the first hybrid line is the control or referenceplant).

4. A plant comprising a recombinant DNA construct (or suppression DNAconstruct): the plant may be assessed or measured relative to a controlplant not comprising the recombinant DNA construct (or suppression DNAconstruct) but otherwise having a comparable genetic background to theplant (e.g., sharing at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%,98%, 99%, or 100% sequence identity of nuclear genetic material comparedto the plant comprising the recombinant DNA construct (or suppressionDNA construct)). There are many laboratory-based techniques availablefor the analysis, comparison and characterization of plant geneticbackgrounds; among these are Isozyme Electrophoresis, RestrictionFragment Length Polymorphisms (RFLPs), Randomly Amplified PolymorphicDNAs (RAPDs), Arbitrarily Primed Polymerase Chain Reaction (AP-PCR), DNAAmplification Fingerprinting (DAF), Sequence Characterized AmplifiedRegions (SCARs), Amplified Fragment Length Polymorphisms (AFLP®s), andSimple Sequence Repeats (SSRs) which are also referred to asMicrosatellites.

Furthermore, one of ordinary skill in the art would readily recognizethat a suitable control or reference plant to be utilized when assessingor measuring an agronomic characteristic or phenotype of a transgenicplant would not include a plant that had been previously selected, viamutagenesis or transformation, for the desired agronomic characteristicor phenotype.

Other Methods

Other methods include but are not limited to methods for increasingnitrogen stress tolerance in a plant, methods for evaluating nitrogenstress tolerance in a plant, methods for altering an agronomiccharacteristic in a plant, methods for determining an alteration of anagronomic characteristic in a plant, and methods for producing seed. Inan embodiment, the plant is a monocotyledonous or dicotyledonous plant,a maize or soybean plant, even more In an embodiment a maize plant. Theplant may also be sunflower, sorghum, canola, wheat, alfalfa, cotton,rice, barley, or millet. The seed is can be a maize or soybean seed amaize seed, and even more In an embodiment, a maize hybrid seed or maizeinbred seed.

Particularly other methods include but are not limited to the following:

A method of increasing nitrogen stress tolerance in a plant, comprising:(a) introducing into a regenerable plant cell a recombinant DNAconstruct comprising a polynucleotide operably linked to at least oneregulatory sequence (in an embodiment a promoter functional in a plant),wherein the polynucleotide encodes a polypeptide having an amino acidsequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%,60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%,74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%,88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%sequence identity, based on the Clustal V method of alignment, whencompared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32; and (b)regenerating a transgenic plant from the regenerable plant cell afterstep (a), wherein the transgenic plant comprises in its genome therecombinant DNA construct and exhibits increased nitrogen stresstolerance when compared to a control plant not comprising therecombinant DNA construct. The method may further comprise (c) obtaininga progeny plant derived from the transgenic plant, wherein said progenyplant comprises in its genome the suppression DNA construct and exhibitsincreased nitrogen tolerance when compared to a control plant notcomprising the recombinant DNA construct.

A method of increasing nitrogen stress tolerance in a plant, comprising:(a) introducing into a regenerable plant cell a suppression DNAconstruct comprising at least one regulatory sequence (in an embodimenta promoter functional in a plant) operably linked to all or part of (i)a nucleic acid sequence encoding a polypeptide having an amino acidsequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%,60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%,74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%,88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%sequence identity, based on the Clustal V method of alignment, whencompared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32, or (ii) a fullcomplement of the nucleic acid sequence of (a)(i); and (b) regeneratinga transgenic plant from the regenerable plant cell after step (a),wherein the transgenic plant comprises in its genome the suppression DNAconstruct and exhibits increased nitrogen stress tolerance when comparedto a control plant not comprising the suppression DNA construct. Themethod may further comprise (c) obtaining a progeny plant derived fromthe transgenic plant, wherein said progeny plant comprises in its genomethe suppression DNA construct and exhibits increased nitrogen tolerancewhen compared to a control plant not comprising the suppression DNAconstruct.

A method of increasing nitrogen stress tolerance in a plant, comprising:(a) introducing into a regenerable plant cell a suppression DNAconstruct comprising at least one regulatory sequence (in an embodimenta promoter functional in a plant) operably linked to a region derivedfrom all or part of a sense strand or antisense strand of a target geneof interest, said region having a nucleic acid sequence of at least 50%,51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%,65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%,79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based onthe Clustal V method of alignment, when compared to said all or part ofa sense strand or antisense strand from which said region is derived,and wherein said target gene of interest encodes an LNT2 or LNT2-likepolypeptide; and (b) regenerating a transgenic plant from theregenerable plant cell after step (a), wherein the transgenic plantcomprises in its genome the suppression DNA construct and exhibitsincreased nitrogen stress tolerance when compared to a control plant notcomprising the suppression DNA construct. The method may furthercomprise (c) obtaining a progeny plant derived from the transgenicplant, wherein said progeny plant comprises in its genome thesuppression DNA construct and exhibits increased nitrogen tolerance whencompared to a control plant not comprising the suppression DNAconstruct.

A method of evaluating nitrogen stress tolerance in a plant, comprising(a) introducing into a regenerable plant cell a recombinant DNAconstruct comprising a polynucleotide operably linked to at least oneregulatory sequence (in an embodiment a promoter functional in a plant),wherein the polynucleotide encodes a polypeptide having an amino acidsequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%,60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%,74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%,88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%sequence identity, based on the Clustal V method of alignment, whencompared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32; (b) regenerating atransgenic plant from the regenerable plant cell after step (a), whereinthe transgenic plant comprises in its genome the recombinant DNAconstruct; and (c) evaluating the transgenic plant for nitrogen stresstolerance compared to a control plant not comprising the recombinant DNAconstruct. The method may further comprise (d) obtaining a progeny plantderived from the transgenic plant, wherein the progeny plant comprisesin its genome the recombinant DNA construct; and (e) evaluating theprogeny plant for nitrogen stress tolerance compared to a control plantnot comprising the recombinant DNA construct.

A method of evaluating nitrogen stress tolerance in a plant, comprising(a) introducing into a regenerable plant cell a suppression DNAconstruct comprising at least one regulatory sequence (in an embodimenta promoter functional in a plant) operably linked to all or part of (i)a nucleic acid sequence encoding a polypeptide having an amino acidsequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%,60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%,74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%,88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%sequence identity, based on the Clustal V method of alignment, whencompared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32; or (ii) a fullcomplement of the nucleic acid sequence of (a)(i); (b) regenerating atransgenic plant from the regenerable plant cell after step (a), whereinthe transgenic plant comprises in its genome the suppression DNAconstruct; and (c) evaluating the transgenic plant for nitrogen stresstolerance compared to a control plant not comprising the suppression DNAconstruct. The method may further comprise (d) obtaining a progeny plantderived from the transgenic plant, wherein the progeny plant comprisesin its genome the suppression DNA construct; and (e) evaluating theprogeny plant for nitrogen stress tolerance compared to a control plantnot comprising the suppression DNA construct.

A method of evaluating nitrogen stress tolerance in a plant, comprising(a) introducing into a regenerable plant cell a suppression DNAconstruct comprising at least one regulatory sequence (in an embodimenta promoter functional in a plant) operably linked to a region derivedfrom all or part of a sense strand or antisense strand of a target geneof interest, said region having a nucleic acid sequence of at least 50%,51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%,65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%,79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based onthe Clustal V method of alignment, when compared to said all or part ofa sense strand or antisense strand from which said region is derived,and wherein said target gene of interest encodes an LNT2 or LNT2-likepolypeptide; (b) regenerating a transgenic plant from the regenerableplant cell after step (a), wherein the transgenic plant comprises in itsgenome the suppression DNA construct; and (c) evaluating the transgenicplant for nitrogen stress tolerance compared to a control plant notcomprising the suppression DNA construct. The method may furthercomprise (d) obtaining a progeny plant derived from the transgenicplant, wherein the progeny plant comprises in its genome the suppressionDNA construct; and (e) evaluating the progeny plant for nitrogen stresstolerance compared to a control plant not comprising the suppression DNAconstruct.

A method of evaluating nitrogen stress tolerance in a plant, comprising(a) introducing into a regenerable plant cell a recombinant DNAconstruct comprising a polynucleotide operably linked to at least oneregulatory sequence (in an embodiment a promoter functional in a plant),wherein said polynucleotide encodes a polypeptide having an amino acidsequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%,60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%,74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%,88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%sequence identity, based on the Clustal V method of alignment, whencompared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32; (b) regenerating atransgenic plant from the regenerable plant cell after step (a), whereinthe transgenic plant comprises in its genome the recombinant DNAconstruct; (c) obtaining a progeny plant derived from said transgenicplant, wherein the progeny plant comprises in its genome the recombinantDNA construct; and (d) evaluating the progeny plant for nitrogen stresstolerance compared to a control plant not comprising the recombinant DNAconstruct.

A method of evaluating nitrogen stress tolerance in a plant, comprising(a) introducing into a regenerable plant cell a suppression DNAconstruct comprising at least one regulatory sequence (in an embodimenta promoter functional in a plant) operably linked to all or part of (i)a nucleic acid sequence encoding a polypeptide having an amino acidsequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%,60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%,74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%,88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%sequence identity, based on the Clustal V method of alignment, whencompared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32; or (ii) a fullcomplement of the nucleic acid sequence of (a)(i); (b) regenerating atransgenic plant from the regenerable plant cell after step (a), whereinthe transgenic plant comprises in its genome the suppression DNAconstruct; (c) obtaining a progeny plant derived from said transgenicplant, wherein the progeny plant comprises in its genome the suppressionDNA construct; and (d) evaluating the progeny plant for nitrogen stresstolerance compared to a control plant not comprising the recombinant DNAconstruct.

A method of evaluating nitrogen stress tolerance in a plant, comprising(a) introducing into a regenerable plant cell a suppression DNAconstruct comprising at least one regulatory sequence (in an embodimenta promoter functional in a plant) operably linked to a region derivedfrom all or part of a sense strand or antisense strand of a target geneof interest, said region having a nucleic acid sequence of at least 50%,51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%,65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%,79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity, based onthe Clustal V method of alignment, when compared to said all or part ofa sense strand or antisense strand from which said region is derived,and wherein said target gene of interest encodes an LNT2 or LNT2-likepolypeptide; (b) regenerating a transgenic plant from the regenerableplant cell after step (a), wherein the transgenic plant comprises in itsgenome the suppression DNA construct; (c) obtaining a progeny plantderived from the transgenic plant, wherein the progeny plant comprisesin its genome the suppression DNA construct; and (d) evaluating theprogeny plant for nitrogen stress tolerance compared to a control plantnot comprising the recombinant DNA construct.

A method of determining an alteration of an agronomic characteristic ina plant, comprising (a) introducing into a regenerable plant cell arecombinant DNA construct comprising a polynucleotide operably linked toat least on regulatory sequence (in an embodiment a promoter functionalin a plant), wherein said polynucleotide encodes a polypeptide having anamino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%,58%, 59%, 60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%,72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%,86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or100% sequence identity, based on the Clustal V method of alignment, whencompared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32; (b) regenerating atransgenic plant from the regenerable plant cell after step (a), whereinthe transgenic plant comprises in its genome said recombinant DNAconstruct; and (c) determining whether the transgenic plant exhibits analteration of at least one agronomic characteristic when compared, in anembodiment under nitrogen limiting conditions, to a control plant notcomprising the recombinant DNA construct. The method may furthercomprise (d) obtaining a progeny plant derived from the transgenicplant, wherein the progeny plant comprises in its genome the recombinantDNA construct; and (e) determining whether the progeny plant exhibits analteration of at least one agronomic characteristic when compared, in anembodiment under nitrogen limiting conditions, to a control plant notcomprising the recombinant DNA construct.

A method of determining an alteration of an agronomic characteristic ina plant, comprising (a) introducing into a regenerable plant cell asuppression DNA construct comprising at least one regulatory sequence(in an embodiment a promoter functional in a plant) operably linked toall or part of (i) a nucleic acid sequence encoding a polypeptide havingan amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%,57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%,71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%,85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%,99%, or 100% sequence identity, based on the Clustal V method ofalignment, when compared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32; or(ii) a full complement of the nucleic acid sequence of (i); (b)regenerating a transgenic plant from the regenerable plant cell afterstep (a), wherein the transgenic plant comprises in its genome thesuppression DNA construct; and (c) determining whether the transgenicplant exhibits an alteration of at least one agronomic characteristicwhen compared, in an embodiment under nitrogen limiting conditions, to acontrol plant not comprising the suppression DNA construct. The methodmay further comprise (d) obtaining a progeny plant derived from thetransgenic plant, wherein the progeny plant comprises in its genome thesuppression DNA construct; and (e) determining whether the progeny plantexhibits an alteration of at least one agronomic characteristic whencompared, in an embodiment under nitrogen limiting conditions, to acontrol plant not comprising the suppression DNA construct.

A method of determining an alteration of an agronomic characteristic ina plant, comprising (a) introducing into a regenerable plant cell asuppression DNA construct comprising at least one regulatory sequence(in an embodiment a promoter functional in a plant) operably linked to aregion derived from all or part of a sense strand or antisense strand ofa target gene of interest, said region having a nucleic acid sequence ofat least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%,62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%,76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%,90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequenceidentity, based on the Clustal V method of alignment, when compared tosaid all or part of a sense strand or antisense strand from which saidregion is derived, and wherein said target gene of interest encodes anLNT2 or LNT2-like polypeptide; (b) regenerating a transgenic plant fromthe regenerable plant cell after step (a), wherein the transgenic plantcomprises in its genome the suppression DNA construct; and (c)determining whether the transgenic plant exhibits an alteration of atleast one agronomic characteristic when compared, in an embodiment undernitrogen limiting conditions, to a control plant not comprising thesuppression DNA construct. The method may further comprise (d) obtaininga progeny plant derived from the transgenic plant, wherein the progenyplant comprises in its genome the suppression DNA construct; and (e)determining whether the progeny plant exhibits an alteration of at leastone agronomic characteristic when compared, in an embodiment undernitrogen limiting conditions, to a control plant not comprising thesuppression DNA construct.

A method of determining an alteration of an agronomic characteristic ina plant, comprising (a) introducing into a regenerable plant cell arecombinant DNA construct comprising a polynucleotide operably linked toat least one regulatory sequence (in an embodiment a promoter functionalin a plant), wherein said polynucleotide encodes a polypeptide having anamino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%,58%, 59%, 60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%,72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%,86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or100% sequence identity, based on the Clustal V method of alignment, whencompared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32; (b) regenerating atransgenic plant from the regenerable plant cell after step (a), whereinthe transgenic plant comprises in its genome said recombinant DNAconstruct; (c) obtaining a progeny plant derived from said transgenicplant, wherein the progeny plant comprises in its genome the recombinantDNA construct; and (d) determining whether the progeny plant exhibits analteration of at least one agronomic characteristic when compared, in anembodiment under nitrogen limiting conditions, to a control plant notcomprising the recombinant DNA construct.

A method of determining an alteration of an agronomic characteristic ina plant, comprising (a) introducing into a regenerable plant cell asuppression DNA construct comprising at least one regulatory sequence(in an embodiment a promoter functional in a plant) operably linked toall or part of (i) a nucleic acid sequence encoding a polypeptide havingan amino acid sequence of at least 50%, 51%, 52%, 53%, 54%, 55%, 56%,57%, 58%, 59%, 60%, 56%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%,71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%,85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%,99%, or 100% sequence identity, based on the Clustal V method ofalignment, when compared to SEQ ID NO:18, 20, 24, 26, 28, 30, or 32; or(ii) a full complement of the nucleic acid sequence of (i); (b)regenerating a transgenic plant from the regenerable plant cell afterstep (a), wherein the transgenic plant comprises in its genome thesuppression DNA construct; (c) obtaining a progeny plant derived fromsaid transgenic plant, wherein the progeny plant comprises in its genomethe suppression DNA construct; and (d) determining whether the progenyplant exhibits an alteration of at least one agronomic characteristicwhen compared, in an embodiment under nitrogen limiting conditions, to acontrol plant not comprising the recombinant DNA construct.

A method of determining an alteration of an agronomic characteristic ina plant, comprising (a) introducing into a regenerable plant cell asuppression DNA construct comprising at least one regulatory sequence(in an embodiment a promoter functional in a plant) operably linked to aregion derived from all or part of a sense strand or antisense strand ofa target gene of interest, said region having a nucleic acid sequence ofat least 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 56%,62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%,76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%,90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequenceidentity, based on the Clustal V method of alignment, when compared tosaid all or part of a sense strand or antisense strand from which saidregion is derived, and wherein said target gene of interest encodes anLNT2 or LNT2-like polypeptide; (b) regenerating a transgenic plant fromthe regenerable plant cell after step (a), wherein the transgenic plantcomprises in its genome the suppression DNA construct; (c) obtaining aprogeny plant derived from said transgenic plant, wherein the progenyplant comprises in its genome the suppression DNA construct; and (d)determining whether the progeny plant exhibits an alteration of at leastone agronomic characteristic when compared, in an embodiment undernitrogen limiting conditions, to a control plant not comprising thesuppression DNA construct.

A method of producing seed (in an embodiment seed that can be sold as anitrogen stress tolerant product offering) comprising any of thepreceding other methods, and further comprising obtaining seeds fromsaid progeny plant, wherein said seeds comprise in their genome saidrecombinant DNA construct (or suppression DNA construct).

In any of the foregoing other methods or any other embodiments ofmethods of the present invention, the step of determining an alterationof an agronomic characteristic in a transgenic plant, if applicable, mayin an embodiment comprise determining whether the transgenic plantexhibits an alteration of at least one agronomic characteristic whencompared, under varying environmental conditions, to a control plant notcomprising the recombinant DNA construct.

In any of the foregoing other methods or any other embodiments ofmethods of the present invention, the step of determining an alterationof an agronomic characteristic in a progeny plant, if applicable, maycomprise determining whether the progeny plant exhibits an alteration ofat least one agronomic characteristic when compared, under varyingenvironmental conditions, to a control plant not comprising therecombinant DNA construct.

In any of the preceding other methods or any other embodiments ofmethods of the present invention, in said introducing step saidregenerable plant cell may comprises a callus cell (in an embodimentembryogenic), a gametic cell, a meristematic cell, or a cell of animmature embryo. The regenerable plant cells are in an embodiment froman inbred maize plant.

In any of the preceding other methods or any other embodiments ofmethods of the present invention, said regenerating step in anembodiment comprises: (i) culturing said transformed plant cells in amedia comprising an embryogenic promoting hormone until callusorganization is observed; (ii) transferring said transformed plant cellsof step (i) to a first media which includes a tissue organizationpromoting hormone; and (iii) subculturing said transformed plant cellsafter step (ii) onto a second media, to allow for shoot elongation, rootdevelopment or both.

In any of the preceding other methods or any other embodiments ofmethods of the present invention, the at least one agronomiccharacteristic is selected from the group consisting of greenness,yield, growth rate, biomass, fresh weight at maturation, dry weight atmaturation, fruit yield, seed yield, total plant nitrogen content, fruitnitrogen content, seed nitrogen content, nitrogen content in avegetative tissue, whole plant amino acid content, vegetative tissuefree amino acid content, fruit free amino acid content, seed free aminoacid content, total plant protein content, fruit protein content, seedprotein content, protein content in a vegetative tissue, droughttolerance, nitrogen uptake, resistance to root lodging, harvest index,stalk lodging, plant height, ear height, and ear length. Yield,greenness and biomass are particularly other agronomic characteristicsfor alteration (in an embodiment an increase).

In any of the preceding other methods or any other embodiments ofmethods of the present invention, the plant in an embodiment exhibitsthe alteration of at least one agronomic characteristic when compared,under nitrogen stress conditions, to a control plant not comprising saidrecombinant DNA construct (or suppression DNA construct).

In any of the preceding other methods or any other embodiments ofmethods of the present invention, alternatives exist for introducinginto a regenerable plant cell a recombinant DNA construct comprising apolynucleotide operably linked to at least one regulatory sequence. Forexample, one may introduce into a regenerable plant cell a regulatorysequence (such as one or more enhancers, in an embodiment as part of atransposable element), and then screen for an event in which theregulatory sequence is operably linked to an endogenous gene encoding apolypeptide of the instant invention.

The introduction of recombinant DNA constructs of the present inventioninto plants may be carried out by any suitable technique, including butnot limited to direct DNA uptake, chemical treatment, electroporation,microinjection, cell fusion, infection, vector mediated DNA transfer,bombardment, or Agrobacterium mediated transformation.

Other techniques are set forth below in the Examples below fortransformation of maize plant cells and soybean plant cells.

Other methods for transforming dicots, primarily by use of Agrobacteriumtumefaciens, and obtaining transgenic plants include those published forcotton (U.S. Pat. No. 5,004,863, U.S. Pat. No. 5,159,135, U.S. Pat. No.5,518,908); soybean (U.S. Pat. No. 5,569,834, U.S. Pat. No. 5,416,011,McCabe et. al., Bio/Technology 6:923 (1988), Christou et al., PlantPhysiol. 87:671 674 (1988)); Brassica (U.S. Pat. No. 5,463,174); peanut(Cheng et al., Plant Cell Rep. 15:653 657 (1996), McKently et al., PlantCell Rep. 14:699 703 (1995)); papaya; and pea (Grant et al., Plant CellRep. 15:254-258 (1995)).

Transformation of monocotyledons using electroporation, particlebombardment, and Agrobacterium have also been reported and are includedas other methods, for example, transformation and plant regeneration asachieved in asparagus (Bytebier et al., Proc. Natl. Acad. Sci. U.S.A.84:5354, (1987)); barley (Wan and Lemaux, Plant Physiol. 104:37 (1994));corn (Rhodes et al., Science 240:204 (1988), Gordon-Kamm et al., PlantCell 2:603 618 (1990), Fromm et al., Bio/Technology 8:833 (1990), Kozielet al., Bio/Technology 11:194 (1993), Armstrong et al., Crop Science35:550-557 (1995)); oat (Somers et al., Bio/Technology 10:1589 (1992));orchard grass (Horn et al., Plant Cell Rep. 7:469 (1988)); rice(Toriyama et al., Theor. Appl. Genet. 205:34 (1986); Part et al., PlantMol. Biol. 32:1135 1148, (1996); Abedinia et al., Aust. J. PlantPhysiol. 24:133 141 (1997); Zhang and Wu, Theor. Appl. Genet. 76:835(1988); Zhang et al., Plant Cell Rep. 7:379, (1988); Battraw and Hall,Plant Sci. 86:191 202 (1992); Christou et al., Bio/Technology 9:957(1991)); rye (De la Pena et al., Nature 325:274 (1987)); sugarcane(Bower and Birch, Plant J. 2:409 (1992)); tall fescue (Wang et al.,Bio/Technology 10:691 (1992)); and wheat (Vasil et al., Bio/Technology10:667 (1992); U.S. Pat. No. 5,631,152).

There are a variety of methods for the regeneration of plants from planttissue. The particular method of regeneration will depend on thestarting plant tissue and the particular plant species to beregenerated.

The regeneration, development, and cultivation of plants from singleplant protoplast transformants or from various transformed explants iswell known in the art (Weissbach and Weissbach, In: Methods for PlantMolecular Biology, (Eds.), Academic Press, Inc. San Diego, Calif.,(1988)). This regeneration and growth process typically includes thesteps of selection of transformed cells, culturing those individualizedcells through the usual stages of embryonic development through therooted plantlet stage. Transgenic embryos and seeds are similarlyregenerated. The resulting transgenic rooted shoots are thereafterplanted in an appropriate plant growth medium such as soil.

The development or regeneration of plants containing the foreign,exogenous isolated nucleic acid fragment that encodes a protein ofinterest is well known in the art. In an embodiment, the regeneratedplants are self-pollinated to provide homozygous transgenic plants.Otherwise, pollen obtained from the regenerated plants is crossed toseed-grown plants of agronomically important lines. Conversely, pollenfrom plants of these important lines is used to pollinate regeneratedplants. A transgenic plant of the present invention containing a desiredpolypeptide is cultivated using methods well known to one skilled in theart.

EXAMPLES

The present invention is further illustrated in the following Examples,in which parts and percentages are by weight and degrees are Celsius,unless otherwise stated. It should be understood that these Examples,while indicating other embodiments of the invention, are given by way ofillustration only. From the above discussion and these Examples, oneskilled in the art can ascertain the essential characteristics of thisinvention, and without departing from the spirit and scope thereof, canmake various changes and modifications of the invention to adapt it tovarious usages and conditions. Furthermore, various modifications of theinvention in addition to those shown and described herein will beapparent to those skilled in the art from the foregoing description.Such modifications are also intended to fall within the scope of theappended claims.

Example 1 Creation of an Arabidopsis Population with Activation-TaggedGenes

An 18.49-kb T-DNA based binary construct was created, pHSbarENDs2 (SEQID NO:1; FIG. 1), that contains four multimerized enhancer elementsderived from the Cauliflower Mosaic Virus 35S promoter (corresponding tosequences −341 to −64, as defined by Odell et al., Nature 313:810-812(1985)). The construct also contains vector sequences (pUC9) and apoly-linker (SEQ ID NO:11) to allow plasmid rescue, transposon sequences(Ds) to remobilize the T-DNA, and the bar gene to allow for glufosinateselection of transgenic plants. In principle, only the 10.8-kb segmentfrom the right border (RB) to left border (LB) inclusive will betransferred into the host plant genome. Since the enhancer elements arelocated near the RB, they can induce cis-activation of genomic locifollowing T-DNA integration.

Arabidopsis activation-tagged populations were created by whole plantAgrobacterium transformation. The pHSbarENDs2 construct was transformedinto Agrobacterium tumefaciens strain C58, grown in lysogeny brothmedium at 25° C. to OD600˜1.0. Cells were then pelleted bycentrifugation and resuspended in an equal volume of 5% sucrose/0.05%Silwet L-77 (OSI Specialties, Inc). At early bolting, soil grownArabidopsis thaliana ecotype Col-0 were top watered with theAgrobacterium suspension. A week later, the same plants were top wateredagain with the same Agrobacterium strain in sucrose/Silwet. The plantswere then allowed to set seed as normal. The resulting T1 seed were sownon soil, and transgenic seedlings were selected by spraying withglufosinate (FINALE®; AgrEvo; Bayer Environmental Science). A total of100,000 glufosinate resistant T1 seedlings were selected. T2 seed fromeach line was kept separate.

Example 2 Screens to Identify Lines with Tolerance to Low Nitrogen

From each of 100,000 separate T1 activation-tagged lines, eleven T2plants are sown on square plates (15 mm×15 mm) containing 0.5×N-FreeHoagland's, 0.4 mM potassium nitrate, 0.1% sucrose, 1 mM MES and 0.25%Phytagel™ (Low N medium). Five lines are plated per plate, and theinclusion of 9 wild-type individuals on each plate makes for a total of64 individuals in an 8×8 grid pattern (see FIG. 11). Plates are kept forthree days in the dark at 4° C. to stratify seeds, and then placedhorizontally for nine days at 22° C. light and 20° C. dark. Photoperiodis sixteen hours light and eight hours dark, with an average lightintensity of ˜200 mmol/m²/s. Plates are rotated and shuffled dailywithin each shelf. At day twelve (nine days of growth), seedling statusis evaluated by imaging the entire plate.

After masking the plate image to remove background color, two differentmeasurements are collected for each individual: total rosette area, andthe percentage of color that falls into a green color bin. Using hue,saturation and intensity data (HSI), the green color bin consists ofhues 50 to 66. Total rosette area is used as a measure of plant biomass,whereas the green color bin was shown by dose-response studies to be anindicator of nitrogen assimilation (see FIG. 12).

Lines with a significant increase in total rosette area and/or greencolor bin, when compared to the wild-type controls, are designated asPhase 1 hits. Phase 1 hits are re-screened in duplicate under the sameassay conditions (Phase 2 screen). A Phase 3 screen is also employed tofurther validate mutants that passed through Phases 1 and 2. In Phase 3,each line is plated separately on Low N medium, such that 32 T2individuals are grown next to 32 wild-type individuals on one plate,providing greater statistical rigor to the analysis. If a line shows asignificant difference from the controls in Phase 3, the line is thenconsidered a validated nitrogen-deficiency tolerant line.

Example 3 Identification of Activation-Taqqed Genes

Genes flanking the T-DNA insert in nitrogen tolerant lines areidentified using one, or both, of the following two standard procedures:(1) thermal asymmetric interlaced (TAIL) PCR (Liu et al., Plant J.8:457-63 (1995)); and (2) SAIFF PCR (Siebert et al., Nucleic Acids Res.23:1087-1088 (1995)). In lines with complex multimerized T-DNA inserts,TAIL PCR and SAIFF PCR may both prove insufficient to identify candidategenes. In these cases, other procedures, including inverse PCR, plasmidrescue and/or genomic library construction, can be employed.

A successful result is one where a single TAIL or SAIFF PCR fragmentcontains a T-DNA border sequence and Arabidopsis genomic sequence. Oncea tag of genomic sequence flanking a T-DNA insert is obtained, candidategenes are identified by alignment to publicly available Arabidopsisgenome sequence. Specifically, the annotated gene nearest the 35Senhancer elements/T-DNA RB are candidates for genes that are activated.

To verify that an identified gene is truly near a T-DNA and to rule outthe possibility that the TAIL/SAIFF fragment is a chimeric cloningartifact, a diagnostic PCR on genomic DNA is done with one oligo in theT-DNA and one oligo specific for the candidate gene. Genomic DNA samplesthat give a PCR product are interpreted as representing a T-DNAinsertion. This analysis also verifies a situation in which more thanone insertion event occurs in the same line, e.g., if multiple differinggenomic fragments are identified in TAIL and/or SAIFF PCR analyses.

Example 4 Identification of Activation-Tagged LNT2 Gene

An activation tagged-line (line 111786) showing nitrogen-deficiencytolerance was further analyzed. DNA from the line was extracted, andgenes flanking the T-DNA insert in the mutant line were identified usingligation-mediated PCR (Siebert et al., Nucleic Acids Res. 23:1087-1088(1995)). A single amplified fragment was identified that contained aT-DNA border sequence and Arabidopsis genomic sequence. Once a tag ofgenomic sequence flanking a T-DNA insert was obtained, a candidate genewas identified by alignment to the completed Arabidopsis genome.Specifically, the annotated gene nearest the 35S enhancer elements/T-DNARB was the candidate for the gene activated in the line. In the case ofline 111786 the gene nearest the 35S enhancers was At5g50930 (SEQ IDNO:27) encoding the Arabidopsis thaliana “unknown protein” referred toherein as LNT2 (SEQ ID NO:28; NCBI GI 15241317).

Example 5 Validation of Candidate Arabidopsis Gene (At5g50930) ViaTransformation into Arabidopsis

Candidate genes can be transformed into Arabidopsis and overexpressedunder the 35S promoter. If the same or similar phenotype is observed inthe transgenic line as in the parent activation-tagged line, then thecandidate gene is considered to be a validated “lead gene” inArabidopsis.

The Arabidopsis At5g50930 gene (SEQ ID NO:27) was tested for its abilityto confer nitrogen-deficiency tolerance in the following manner.

The At5g50930 cDNA was amplified by RT-PCR with the following primers:

1. At5g50930-5′ attB forward primer (SEQ ID NO:35)

The forward primer contains the attB1 sequence(ACAAGTTTGTACAAAAAAGCAGGCT; SEQ ID NO:12) and a consensus Kozak sequence(CAACA) upstream of the first 21 nucleotides of the protein-codingregion, beginning with the ATG start codon, of said cDNA.

2. At5g50930-3′ attB reverse primer (SEQ ID NO:36)

The reverse primer contains the attB2 sequence(ACCACTTTGTACAAGAAAGCTGGGT; SEQ ID NO:13) adjacent to the reversecomplement of the last 21 nucleotides of the protein-coding region,beginning with the reverse complement of the stop codon, of said cDNA.

The RT-PCR reaction yielded two products, referred to herein as Int2-2and Int2-3 (SEQ ID NOs:29 and 31, respectively). The products wereidentified as splice variants of the At5g50930 gene.

Using the INVITROGEN™ GATEWAY® CLONASE™ technology, a BP RecombinationReaction was performed for each RT-PCR product with pDONR™Zeo (SEQ IDNO:2; FIG. 2). This process removes the bacteria lethal ccdB gene, aswell as the chloramphenicol resistance gene (CAM), from pDONR™Zeo anddirectionally clones the PCR product with flanking attB1 and attB2sites, creating an entry clone. One positively identified entry clonefor each splice variant sequence was used for a subsequent LRRecombination Reaction with a destination vector, as follows.

A 16.8-kb T-DNA based binary vector (destination vector), calledpBC-yellow (SEQ ID NO:4; FIG. 4), was constructed with a 1.3-kb 35Spromoter immediately upstream of the INVITROGEN™ GATEWAY C1 conversioninsert, which contains the bacterial lethal ccdB gene as well as thechloramphenicol resistance gene (CAM) flanked by attR1 and attR2sequences. The vector also contains the RD29a promoter drivingexpression of the gene for ZS-Yellow (INVITROGEN™), which confers yellowfluorescence to transformed seed. Using the INVITROGEN™ GATEWAY®technology, an LR Recombination Reaction was performed with the entryclone containing Int2-2 and the pBC-yellow vector. This amplificationallowed for rapid and directional cloning of Int2-2 (SEQ ID NO: 29)behind the 35S promoter in pBC-yellow. An LR Recombination Reaction wasalso performed with the entry clone containing Int2-3 and the pBC-yellowvector.

Applicants then introduced the 35S promoter:At5g50930 expressionconstructs into wild-type Arabidopsis ecotype Col-0, using the sameAgrobacterium-mediated transformation procedure described in Example 1.Transgenic T1 seeds were selected by yellow fluorescence, and 32 ofthese T1 seeds were plated next to 32 wild-type Arabidopsis ecotypeCol-0 seeds on low nitrogen medium. All subsequent growth and imagingconditions were performed as described in Example 1. It was found thatthe original phenotype from activation tagging, tolerance to nitrogenlimiting conditions, could be recapitulated in wild-type Arabidopsisplants that were transformed with a construct where an At5g50930 genewas directly expressed by the 35S promoter.

Example 6 Composition of cDNA Libraries, Isolation and Sequencing ofcDNA Clones

cDNA libraries may be prepared by any one of many methods available. Forexample, the cDNAs may be introduced into plasmid vectors by firstpreparing the cDNA libraries in UNI-ZAP™ XR vectors according to themanufacturer's protocol (Stratagene Cloning Systems, La Jolla, Calif.).The UNI-ZAP™ XR libraries are converted into plasmid libraries accordingto the protocol provided by Stratagene. Upon conversion, cDNA insertswill be contained in the plasmid vector pBLUESCRIPT®. In addition, thecDNAs may be introduced directly into precut BLUESCRIPT® II SK(+)vectors (Stratagene) using T4 DNA ligase (New England Biolabs), followedby transfection into DH10B cells according to the manufacturer'sprotocol (GIBCO BRL Products). Once the cDNA inserts are in plasmidvectors, plasmid DNAs are prepared from randomly picked bacterialcolonies containing recombinant pBLUESCRIPT® plasmids, or the insertcDNA sequences are amplified via polymerase chain reaction using primersspecific for vector sequences flanking the inserted cDNA sequences.Amplified insert DNAs or plasmid DNAs are sequenced in dye-primersequencing reactions to generate partial cDNA sequences (expressedsequence tags or “ESTs”; see Adams et al., Science 252:1651-1656(1991)). The resulting ESTs are analyzed using a Perkin Elmer Model 377fluorescent sequencer.

Full-insert sequence (FIS) data is generated utilizing a modifiedtransposition protocol. Clones identified for FIS are recovered fromarchived glycerol stocks as single colonies, and plasmid DNAs areisolated via alkaline lysis. Isolated DNA templates are reacted withvector primed M13 forward and reverse oligonucleotides in a PCR-basedsequencing reaction and loaded onto automated sequencers. Confirmationof clone identification is performed by sequence alignment to theoriginal EST sequence from which the FIS request is made.

Confirmed templates are transposed via the Primer Island transpositionkit (PE Applied Biosystems, Foster City, Calif.) which is based upon theSaccharomyces cerevisiae Ty1 transposable element (Devine and Boeke,Nucleic Acids Res. 22:3765-3772 (1994)). The in vitro transpositionsystem places unique binding sites randomly throughout a population oflarge DNA molecules. The transposed DNA is then used to transform DH10Belectro-competent cells (GIBCO BRL/Life Technologies, Rockville, Md.)via electroporation. The transposable element contains an additionalselectable marker (named DHFR; Fling and Richards, Nucleic Acids Res.11:5147-5158 (1983)), allowing for dual selection on agar plates of onlythose subclones containing the integrated transposon. Multiple subclonesare randomly selected from each transposition reaction, plasmid DNAs areprepared via alkaline lysis, and templates are sequenced (ABI PRISMdye-terminator ReadyReaction mix) outward from the transposition eventsite, utilizing unique primers specific to the binding sites within thetransposon.

Sequence data is collected (ABI PRISM® Collections) and assembled usingPhred and Phrap (Ewing et al., Genome Res. 8:175-185 (1998); Ewing etal., Genome Res. 8:186-194 (1998)). Phred is a public domain softwareprogram which re-reads the ABI sequence data, re-calls the bases,assigns quality values, and writes the base calls and quality valuesinto editable output files. The Phrap sequence assembly program usesthese quality values to increase the accuracy of the assembled sequencecontigs. Assemblies are viewed by the Consed sequence editor (Gordon etal., Genome Res. 8:195-202 (1998)).

In some of the clones the cDNA fragment corresponds to a portion of the3′-terminus of the gene and does not cover the entire open readingframe. In order to obtain the upstream information one of two differentprotocols is used. The first of these methods results in the productionof a fragment of DNA containing a portion of the desired gene sequencewhile the second method results in the production of a fragmentcontaining the entire open reading frame. Both of these methods use tworounds of PCR amplification to obtain fragments from one or morelibraries. The libraries sometimes are chosen based on previousknowledge that the specific gene should be found in a certain tissue andsometimes are randomly-chosen. Reactions to obtain the same gene may beperformed on several libraries in parallel or on a pool of libraries.Library pools are normally prepared using from 3 to 5 differentlibraries and normalized to a uniform dilution. In the first round ofamplification both methods use a vector-specific (forward) primercorresponding to a portion of the vector located at the 5′-terminus ofthe clone coupled with a gene-specific (reverse) primer. The firstmethod uses a sequence that is complementary to a portion of the alreadyknown gene sequence while the second method uses a gene-specific primercomplementary to a portion of the 3′-untranslated region (also referredto as UTR). In the second round of amplification a nested set of primersis used for both methods. The resulting DNA fragment is ligated into apBLUESCRIPT® vector using a commercial kit and following themanufacturer's protocol. This kit is selected from many available fromseveral vendors including INVITROGEN™ (Carlsbad, Calif.), PromegaBiotech (Madison, Wis.), and GIBCO-BRL (Gaithersburg, Md.). The plasmidDNA is isolated by alkaline lysis method and submitted for sequencingand assembly using Phred/Phrap, as above.

Example 7 Identification of cDNA Clones

cDNA clones encoding LNT2-like polypeptides are identified by conductingBLAST (Basic Local Alignment Search Tool; Altschul et al., J. Mol. Biol.215:403-410 (1993); see also the explanation of the BLAST algorithm onthe world wide web site for the National Center for BiotechnologyInformation at the National Library of Medicine of the NationalInstitutes of Health) searches for similarity to amino acid sequencescontained in the BLAST “nr” database (comprising all non-redundantGenBank CDS translations, sequences derived from the 3-dimensionalstructure Brookhaven Protein Data Bank, the last major release of theSWISS-PROT protein sequence database, EMBL, and DDBJ databases). The DNAsequences from clones can be translated in all reading frames andcompared for similarity to all publicly available protein sequencescontained in the “nr” database using the BLASTX algorithm (Gish andStates, Nat. Genet. 3:266-272 (1993)) provided by the NCBI. Thepolypeptides encoded by the cDNA sequences can be analyzed forsimilarity to all publicly available amino acid sequences contained inthe “nr” database using the BLASTP algorithm provided by the NationalCenter for Biotechnology Information (NCBI). For convenience, theP-value (probability) or the E-value (expectation) of observing a matchof a cDNA-encoded sequence to a sequence contained in the searcheddatabases merely by chance as calculated by BLAST are reported herein as“pLog” values, which represent the negative of the logarithm of thereported P-value or E-value. Accordingly, the greater the pLog value,the greater the likelihood that the cDNA-encoded sequence and the BLAST“hit” represent homologous proteins.

EST sequences can be compared to the GenBank database as describedabove. ESTs that contain sequences more 5- or 3-prime can be found byusing the BLASTN algorithm (Altschul et al., Nucleic Acids Res.25:3389-3402 (1997)) against the Dupont proprietary database comparingnucleotide sequences that share common or overlapping regions ofsequence homology. Where common or overlapping sequences exist betweentwo or more nucleic acid fragments, the sequences can be assembled intoa single contiguous nucleotide sequence, thus extending the originalfragment in either the 5 or 3 prime direction. Once the most 5-prime ESTis identified, its complete sequence can be determined by Full InsertSequencing.

Homologous genes belonging to different species can be found bycomparing the amino acid sequence of a known gene (from either aproprietary source or a public database) against an EST database usingthe tBLASTn algorithm. The tBLASTn algorithm searches an amino acidquery against a nucleotide database that is translated in all 6 readingframes. This search allows for differences in nucleotide codon usagebetween different species, and for codon degeneracy.

Example 8 Characterization of cDNA Clones Encoding LNT2-likePolypeptides

cDNA libraries representing mRNAs from various tissues of Zea mays(maize), Oryza sativa (rice), and Glycine max (soybean) were prepared.The characteristics of the libraries are described below.

TABLE 2 cDNA Libraries from Maize, Rice, and Soybean Library Description(tissue) Clone cpg1c Corn (Zea mays L.) pooled BMS treatedcpg1c.pk013.o6:fis with chemicals related to RNA, DNA synthesis rca1nRice (Oryza sativa L., Nipponbare) callus rca1n.pk001.f6:fis normalizedsfl1n1 Soybean (Glycine max L., Wye) immature sfl1n1.pk002.j1 flowernormalized. sds1f Soybean (Glycine max, Wye) 11 day old sds1f.pk001.k5seedling full length library using trehalose

As shown in Table 3, FIGS. 14A-14B, and FIG. 15, cDNAs identified inTable 2 encode polypeptides similar to the LNT2 polypeptide fromArabidopsis thaliana (At5g50930; NCBI General Identifier No. 15241317;SEQ ID NO:28) and to the LNT2-like polypeptides from Oryza sativa (GINo. 38347162 corresponding to SEQ ID NO: 33) and from Vitis vinifera (GINo. 147791927 corresponding to SEQ ID NO: 34).

Shown in Table 3 (non-patent literature) and Table 4 (patent literature)are the BLASTP results for individual ESTs (“EST”), the sequences of theentire cDNA inserts comprising the indicated cDNA clones (“FIS”), thesequences of contigs assembled from two or more EST, FIS or PCRsequences (“Contig”), or sequences encoding an entire or functionalprotein derived from an FIS or a contig (“CGS”). Also shown in Tables 3and 4 are the percent sequence identity values for each pair of aminoacid sequences using the Clustal V method of alignment with defaultparameters (described below).

TABLE 3 BLASTP Results for Polypeptides Homologous to LNT2 PolypeptidesBLAST Sequence % pLog (SEQ ID NO: #) CStatus NCBI GI No. identity Scorecpg1c.pk013.o6:fis CGS  38347162 77.4 17.8 (SEQ ID NO: 18) (SEQ ID: 33)rca1n.pk001.f6:fis CGS  38347162 100.0 15.8 (SEQ ID NO: 20) (SEQ ID: 33)PSO415619 contig 147791927 58.7 13.0 (SEQ ID NO: 24) (SEQ ID: 34)PSO415620 contig 147791927 57.1 11.8 (SEQ ID NO: 26) (SEQ ID: 34)

TABLE 4 BLASTP Results for Polypeptides Homologous to LNT2 PolypeptidesBLAST Sequence % pLog (SEQ ID NO: #) Status Reference Identity scorecpg1c.pk013.o6:fis CGS SEQ ID NO: 224380 92.3 21.0 (SEQ ID NO: 18) InUS2004214272-A1 rca1n.pk001.f6:fis CGS SEQ ID NO: 188525 100.0 15.7 (SEQID NO: 20) In US2004123343-A1 PSO415619 contig SEQ ID NO: 183694 92.121.4 (SEQ ID NO: 24) In US2004031072-A1 PSO415620 contig SEQ ID NO:183694 84.9 19.8 (SEQ ID NO: 26) In US2004031072-A1

FIGS. 14A and 14B present an alignment of the amino acid sequences setforth in SEQ ID NOs:18, 20, 24, 26, and the amino acid sequences of theLNT2 (At5g50930; NCBI General Identifier No. 15241317), LNT2-2, andLNT2-3 polypeptides from Arabidopsis thaliana (SEQ ID NOs: 28, 30, and32, respectively). Also included in the alignment are the LNT2-likepolypeptides from Oryza sativa (GI No. 38347162 corresponding to SEQ IDNO: 33) and from Vitis vinifera (GI No. 147791927 corresponding to SEQID NO: 34). FIG. 15 is a chart of the percent sequence identity and thedivergence values for each pair of amino acids sequences presented inFIGS. 14A and 14B.

Sequence alignments and percent identity calculations were performedusing the MEGALIGN® program of the LASERGENE® bioinformatics computingsuite (DNASTAR® Inc., Madison, Wis.). Multiple alignment of thesequences was performed using the Clustal method of alignment (Higginsand Sharp (1989) CABIOS. 5:151-153) with the default parameters (GAPPENALTY=10, GAP LENGTH PENALTY=10). Default parameters for pairwisealignments using the Clustal method were KTUPLE 1, GAP PENALTY=3,WINDOW=5 and DIAGONALS SAVED=5.

Example 9 Preparation of a Plant Expression Vector Containing a Homologto the Arabidopsis Lead Gene

Sequences homologous to the lead LNT2 genes can be identified usingsequence comparison algorithms such as BLAST (Basic Local AlignmentSearch Tool; Altschul et al., J. Mol. Biol. 215:403-410 (1993); see alsothe explanation of the BLAST algorithm on the world wide web site forthe National Center for Biotechnology Information at the NationalLibrary of Medicine of the National Institutes of Health). HomologousLNT2-like sequences, such as the ones described in Example 8, can bePCR-amplified by either of the following methods.

Method 1 (RNA-based): If the 5′ and 3′ sequence information for theprotein-coding region of an LNT2 homolog is available, gene-specificprimers can be designed as outlined in Example 5. RT-PCR can be usedwith plant RNA to obtain a nucleic acid fragment containing theprotein-coding region flanked by attB1 (SEQ ID NO:12) and attB2 (SEQ IDNO:13) sequences. The primer may contain a consensus Kozak sequence(CAACA) upstream of the start codon.

Method 2 (DNA-based): Alternatively, if a cDNA clone is available forthe LNT2 homolog, the entire cDNA insert (containing 5′ and 3′non-coding regions) can be PCR amplified. Forward and reverse primerscan be designed that contain either the attB1 sequence andvector-specific sequence that precedes the cDNA insert or the attB2sequence and vector-specific sequence that follows the cDNA insert,respectively. For a cDNA insert cloned into the vector pBLUESCRIPT SK+,the forward primer VC062 (SEQ ID NO:15) and the reverse primer VC063(SEQ ID NO:16) can be used.

Methods 1 and 2 can be modified according to procedures known by oneskilled in the art. For example, the primers of Method 1 may containrestriction sites instead of attB1 and attB2 sites, for subsequentcloning of the PCR product into a vector containing attB1 and attB2sites. Additionally, Method 2 can involve amplification from a cDNAclone, a lambda clone, a BAC clone or genomic DNA.

A PCR product obtained by either method above can be combined with theGATEWAY® donor vector, such as pDONR™Zeo (SEQ ID NO:2; FIG. 2) orpDONR™221 (SEQ ID NO:3; FIG. 3), using a BP Recombination Reaction. Thisprocess removes the bacteria lethal ccdB gene, as well as thechloramphenicol resistance gene (CAM) from pDONR™Zeo or pDONR™221 anddirectionally clones the PCR product with flanking attB1 and attB2 sitesto create an entry clone. Using the INVITROGEN™ GATEWAY® CLONASE™technology, the sequence encoding the homologous LNT2 polypeptide fromthe entry clone can then be transferred to a suitable destinationvector, such as pBC-Yellow (SEQ ID NO:4; FIG. 4), PHP27840 (SEQ ID NO:5;FIG. 5), or PHP23236 (SEQ ID NO:6; FIG. 6), to obtain a plant expressionvector for use with Arabidopsis, soybean, and corn, respectively.

The attP1 and attP2 sites of donor vectors pDONR™/Zeo or pDONR™221 areshown in FIGS. 2 and 3, respectively. The attR1 and attR2 sites ofdestination vectors pBC-Yellow, PHP27840, and PHP23236 are shown inFIGS. 4, 5 and 6, respectively.

Alternatively a MultiSite GATEWAY® LR recombination reaction betweenmultiple entry clones and a suitable destination vector can be performedto create an expression vector.

Example 10 Preparation of Soybean Expression Vectors and Transformationof Soybean with Validated Arabidopsis Lead Genes

Soybean plants can be transformed to overexpress each validatedArabidopsis gene or the corresponding homologs from various species inorder to examine the resulting phenotype.

The same GATEWAY® entry clone described in Example 5 can be used todirectionally clone each gene into the PHP27840 vector (SEQ ID NO:5;FIG. 5) such that expression of the gene is under control of the SCP1promoter.

Soybean embryos may then be transformed with the expression vectorcomprising sequences encoding the instant polypeptides.

To induce somatic embryos, cotyledons, 3-5 mm in length dissected fromsurface sterilized, immature seeds of the soybean cultivar A2872, can becultured in the light or dark at 26° C. on an appropriate agar mediumfor six to ten weeks. Somatic embryos, which produce secondary embryos,are then excised and placed into a suitable liquid medium. Afterrepeated selection for clusters of somatic embryos which multiply asearly, globular staged embryos, the suspensions are maintained asdescribed below.

Soybean embryogenic suspension cultures can be maintained in 35 mLliquid media on a rotary shaker, 150 rpm, at 26° C. with florescentlights on a 16:8 hour day/night schedule. Cultures are subcultured everytwo weeks by inoculating approximately 35 mg of tissue into 35 mL ofliquid medium.

Soybean embryogenic suspension cultures may then be transformed by themethod of particle gun bombardment (Klein et al., Nature (London)327:70-73 (1987), U.S. Pat. No. 4,945,050). A DUPONT BIOLISTIC™PDS1000/HE instrument (helium retrofit) can be used for thesetransformations.

A selectable marker gene which can be used to facilitate soybeantransformation is a chimeric gene composed of the 35S promoter fromcauliflower mosaic virus (Odell et al., Nature 313:810-812 (1985)), thehygromycin phosphotransferase gene from plasmid pJR225 (from E. coli;Gritz et al., Gene 25:179-188 (1983)) and the 3′ region of the nopalinesynthase gene from the T-DNA of the Ti plasmid of Agrobacteriumtumefaciens. Another selectable marker gene which can be used tofacilitate soybean transformation is an herbicide-resistant acetolactatesynthase (ALS) gene from soybean or Arabidopsis. ALS is the first commonenzyme in the biosynthesis of the branched-chain amino acids valine,leucine and isoleucine. Mutations in ALS have been identified thatconvey resistance to some or all of three classes of inhibitors of ALS(U.S. Pat. No. 5,013,659; the entire contents of which are hereinincorporated by reference). Expression of the herbicide-resistant ALSgene can be under the control of a SAM synthetase promoter (U.S. PatentApplication No. US-2003-0226166-A1; the entire contents of which areherein incorporated by reference).

To 50 μL of a 60 mg/mL 1 μm gold particle suspension is added (inorder): 5 μL DNA (1 μg/μL), 20 μL spermidine (0.1 M), and 50 μL CaCl₂(2.5 M). The particle preparation is then agitated for three minutes,spun in a microfuge for 10 seconds and the supernatant removed. TheDNA-coated particles are then washed once in 400 μL 70% ethanol andresuspended in 40 μL of anhydrous ethanol. The DNA/particle suspensioncan be sonicated three times for one second each. Five μL of theDNA-coated gold particles are then loaded on each macro carrier disk.

Approximately 300-400 mg of a two-week-old suspension culture is placedin an empty 60×15 mm petri dish and the residual liquid removed from thetissue with a pipette. For each transformation experiment, approximately5-10 plates of tissue are normally bombarded. Membrane rupture pressureis set at 1100 psi and the chamber is evacuated to a vacuum of 28 inchesmercury. The tissue is placed approximately 3.5 inches away from theretaining screen and bombarded three times. Following bombardment, thetissue can be divided in half and placed back into liquid and culturedas described above.

Five to seven days post bombardment, the liquid media may be exchangedwith fresh media, and eleven to twelve days post bombardment, with freshmedia containing 50 mg/mL hygromycin. This selective media can berefreshed weekly. Seven to eight weeks post bombardment, green,transformed tissue may be observed growing from untransformed, necroticembryogenic clusters. Isolated green tissue is removed and inoculatedinto individual flasks to generate new, clonally propagated, transformedembryogenic suspension cultures. Each new line may be treated as anindependent transformation event. These suspensions can then besubcultured and maintained as clusters of immature embryos orregenerated into whole plants by maturation and germination ofindividual somatic embryos.

Soybean plants transformed with validated genes can be assayed to studyagronomic characteristics relative to control or reference plants. Forexample, yield enhancement and/or stability under low and high nitrogenconditions (e.g., nitrogen limiting conditions and nitrogen-sufficientconditions) can be assayed.

Example 11 Transformation of Maize with Validated Arabidopsis Lead GenesUsing Particle Bombardment

Maize plants can be transformed to overexpress a validated Arabidopsislead gene or the corresponding homologs from various species in order toexamine the resulting phenotype.

The same GATEWAY® entry clones described in Example 5 can be used todirectionally clone each respective gene into a maize transformationvector. Expression of the gene in the maize transformation vector can beunder control of a constitutive promoter such as the maize ubiquitinpromoter (Christensen et al., Plant Mol. Biol. 12:619-632 (1989) andChristensen et al., Plant Mol. Biol. 18:675-689 (1992))

The recombinant DNA construct described above can then be introducedinto maize cells by the following procedure. Immature maize embryos canbe dissected from developing caryopses derived from crosses of theinbred maize lines H99 and LH132. The embryos are isolated ten to elevendays after pollination when they are 1.0 to 1.5 mm long. The embryos arethen placed with the axis-side facing down and in contact withagarose-solidified N6 medium (Chu et al., Sci. Sin. Peking 18:659-668(1975)). The embryos are kept in the dark at 27° C. Friable embryogeniccallus consisting of undifferentiated masses of cells with somaticproembryoids and embryoids borne on suspensor structures proliferatesfrom the scutellum of these immature embryos. The embryogenic callusisolated from the primary explant can be cultured on N6 medium andsub-cultured on this medium every two to three weeks.

The plasmid, p35S/Ac (obtained from Dr. Peter Eckes, Hoechst Ag,Frankfurt, Germany) may be used in transformation experiments in orderto provide for a selectable marker. This plasmid contains the pat gene(see European Patent Publication 0 242 236) which encodesphosphinothricin acetyl transferase (PAT). The enzyme PAT confersresistance to herbicidal glutamine synthetase inhibitors such asphosphinothricin. The pat gene in p35S/Ac is under the control of the35S promoter from cauliflower mosaic virus (Odell et al., Nature313:810-812 (1985)) and the 3′ region of the nopaline synthase gene fromthe T-DNA of the Ti plasmid of Agrobacterium tumefaciens.

The particle bombardment method (Klein et al., Nature 327:70-73 (1987))may be used to transfer genes to the callus culture cells. According tothis method, gold particles (1 μm in diameter) are coated with DNA usingthe following technique. Ten μg of plasmid DNAs are added to 50 μL of asuspension of gold particles (60 mg per mL). Calcium chloride (50 μL ofa 2.5 M solution) and spermidine free base (20 μL of a 1.0 M solution)are added to the particles. The suspension is vortexed during theaddition of these solutions. After ten minutes, the tubes are brieflycentrifuged (5 sec at 15,000 rpm) and the supernatant removed. Theparticles are resuspended in 200 μL of absolute ethanol, centrifugedagain and the supernatant removed. The ethanol rinse is performed againand the particles resuspended in a final volume of 30 μL of ethanol. Analiquot (5 μL) of the DNA-coated gold particles can be placed in thecenter of a KAPTON™ flying disc (Bio-Rad Labs). The particles are thenaccelerated into the maize tissue with a BIOLISTIC™ PDS-1000/He (Bio-RadInstruments, Hercules Calif.), using a helium pressure of 1000 psi, agap distance of 0.5 cm and a flying distance of 1.0 cm.

For bombardment, the embryogenic tissue is placed on filter paper overagarose-solidified N6 medium. The tissue is arranged as a thin lawn andcovers a circular area of about 5 cm in diameter. The petri dishcontaining the tissue can be placed in the chamber of the PDS-1000/Heapproximately 8 cm from the stopping screen. The air in the chamber isthen evacuated to a vacuum of 28 inches of Hg. The macrocarrier isaccelerated with a helium shock wave using a rupture membrane thatbursts when the He pressure in the shock tube reaches 1000 psi.

Seven days after bombardment the tissue can be transferred to N6 mediumthat contains bialaphos (5 mg per liter) and lacks casein or proline.The tissue continues to grow slowly on this medium. After an additionaltwo weeks the tissue can be transferred to fresh N6 medium containingbialaphos. After six weeks, areas of about 1 cm in diameter of activelygrowing callus can be identified on some of the plates containing thebialaphos-supplemented medium. These calli may continue to grow whensub-cultured on the selective medium.

Plants can be regenerated from the transgenic callus by firsttransferring clusters of tissue to N6 medium supplemented with 0.2 mgper liter of 2,4-D. After two weeks the tissue can be transferred toregeneration medium (Fromm et al., Bio/Technology 8:833-839 (1990)).

Transgenic TO plants can be regenerated and their phenotype determinedfollowing HTP procedures. T1 seed can be collected.

T1 plants can be grown under nitrogen limiting conditions, for example 1mM nitrate, and analyzed for phenotypic changes. The followingparameters can be quantified using image analysis: plant area, volume,growth rate and color analysis can be collected and quantified.Overexpression constructs that result in an alteration, compared tosuitable control plants, in greenness (green color bin), yield, growthrate, biomass, fresh or dry weight at maturation, fruit or seed yield,total plant nitrogen content, fruit or seed nitrogen content, nitrogencontent in vegetative tissue, free amino acid content in the wholeplant, free amino acid content in vegetative tissue, free amino acidcontent in the fruit or seed, protein content in the fruit or seed, orprotein content in a vegetative tissue can be considered evidence thatthe Arabidopsis lead gene functions in maize to enhance tolerance tonitrogen deprivation (increased nitrogen tolerance). Furthermore, arecombinant DNA construct containing a validated Arabidopsis gene can beintroduced into a maize inbred line either by direct transformation orintrogression from a separately transformed line.

Example 12 Electroporation of Agrobacterium tumefaciens LBA4404 GeneralDescription

Electroporation competent cells (40 μL), such as Agrobacteriumtumefaciens LBA4404 (containing PHP10523), are thawed on ice (20-30min). PHP10523 contains VIR genes for T-DNA transfer, an Agrobacteriumlow copy number plasmid origin of replication, a tetracycline resistancegene, and a Cos site for in vivo DNA bimolecular recombination.Meanwhile the electroporation cuvette is chilled on ice. Theelectroporator settings are adjusted to 2.1 kV. A DNA aliquot (0.5 μLparental DNA at a concentration of 0.2 μg-1.0 μg in low salt buffer ortwice distilled H₂O) is mixed with the thawed Agrobacterium tumefaciensLBA4404 cells while still on ice. The mixture is transferred to thebottom of electroporation cuvette and kept at rest on ice for 1-2 min.The cells are electroporated (Eppendorf electroporator 2510) by pushingthe “pulse” button twice (ideally achieving a 4.0 millisecond pulse).Subsequently, 0.5 mL of room temperature 2×YT medium (or SOC medium) areadded to the cuvette and transferred to a 15 mL snap-cap tube (e.g.,FALCON™ tube). The cells are incubated at 28-30° C., 200-250 rpm for 3h.

Aliquots of 250 μL are spread onto plates containing YM medium and 50μg/mL spectinomycin and incubated three days at 28-30° C. To increasethe number of transformants one of two optional steps can be performed:

Option 1: Overlay plates with 30 μL of 15 mg/mL rifampicin. LBA4404 hasa chromosomal resistance gene for rifampicin. This additional selectioneliminates some contaminating colonies observed when using poorerpreparations of LBA4404 competent cells.

Option 2: Perform two replicates of the electroporation to compensatefor poorer electrocompetent cells.

Identification of Transformants:

Four independent colonies are picked and streaked on plates containingAB minimal medium and 50 μg/mL spectinomycin for isolation of singlecolonies. The plates are incubated at 28° C. for two to three days. Asingle colony for each putative cointegrate is picked and inoculatedwith 4 mL of 10 g/L bactopeptone, 10 g/L yeast extract, 5 g/L sodiumchloride, and 50 mg/L spectinomycin. The mixture is incubated for 24 hat 28° C. with shaking. Plasmid DNA from 4 mL of culture is isolatedusing QIAGEN Miniprep and an optional Buffer PB wash. The DNA is elutedin 30 μL. Aliquots of 2 μL are used to electroporate 20 μL of DH10b+20μL of twice distilled H₂O as per above. Optionally a 15 μL aliquot canbe used to transform 75-100 μL of INVITROGEN™ Library Efficiency DH5α.The cells are spread on plates containing LB medium and 50 μg/mLspectinomycin and incubated at 37° C. overnight.

Three to four independent colonies are picked for each putativecointegrate and inoculated 4 mL of 2×YT medium (10 g/L bactopeptone, 10g/L yeast extract, 5 g/L sodium chloride) with 50 μg/mL spectinomycin.The cells are incubated at 37° C. overnight with shaking. Next, theplasmid DNA is isolated from 4 mL of culture using QIAprep® Miniprepwith optional Buffer PB wash (elute in 50 μL). 8 μL are used fordigestion with SalI (using parental DNA and PHP10523 as controls). Threemore digestions using restriction enzymes BamHI, EcoRI, and HindIII areperformed for 4 plasmids that represent 2 putative cointegrates withcorrect SalI digestion pattern (using parental DNA and PHP10523 ascontrols). Electronic gels are recommended for comparison.

Alternatively, for high throughput applications, such as that describedfor Gaspe Flint Derived Maize Lines (Example 16), instead of evaluatingthe resulting cointegrate vectors by restriction analysis, threecolonies can be simultaneously used for the infection step as describedin Example 13 (transformation via Agrobacterium).

Example 13 Transformation of Maize Using Agrobacterium

Maize plants can be transformed to overexpress a validated Arabidopsislead gene or the corresponding homologs from various species in order toexamine the resulting phenotype.

Agrobacterium-mediated transformation of maize is performed essentiallyas described by Zhao et al., in Meth. Mol. Biol. 318:315-323 (2006) (seealso Zhao et al., Mol. Breed. 8:323-333 (2001) and U.S. Pat. No.5,981,840 issued Nov. 9, 1999, incorporated herein by reference). Thetransformation process involves bacterium inoculation, co-cultivation,resting, selection, and plant regeneration.

1. Immature Embryo Preparation:

Immature maize embryos are dissected from caryopses and placed in a 2 mLmicrotube containing 2 mL PHI-A medium.

2. Agrobacterium Infection and Co-Cultivation of Immature Embryos: 2.1Infection Step:

PHI-A medium of (1) is removed with 1 mL micropipettor, and 1 mL ofAgrobacterium suspension is added. The tube is gently inverted to mix.The mixture is incubated for 5 min at room temperature.

2.2 Co-culture Step:

The Agrobacterium suspension is removed from the infection step with a 1mL micropipettor. Using a sterile spatula the embryos are scraped fromthe tube and transferred to a plate of PHI-B medium in a 100×15 mm Petridish. The embryos are oriented with the embryonic axis down on thesurface of the medium. Plates with the embryos are cultured at 20° C.,in darkness, for three days. L-Cysteine can be used in theco-cultivation phase. With the standard binary vector, theco-cultivation medium supplied with 100-400 mg/L L-cysteine is criticalfor recovering stable transgenic events.

3. Selection of Putative Transgenic Events:

To each plate of PHI-D medium in a 100×15 mm Petri dish, 10 embryos aretransferred, maintaining orientation, and the dishes are sealed withparafilm. The plates are incubated in darkness at 28° C. Activelygrowing putative events, evinced as pale yellow embryonic tissue, areexpected to be visible in six to eight weeks. Embryos that produce noevents may be brown and necrotic, and little friable tissue growth isevident. Putative transgenic embryonic tissue is sub-cultured to freshPHI-D plates at two-three week intervals, depending on growth rate. Theevents are recorded.

4. Regeneration of TO plants:

Embryonic tissue propagated on PHI-D medium is subcultured to PHI-Emedium (somatic embryo maturation medium), in 100×25 mm Petri dishes andincubated at 28° C., in darkness, until somatic embryos mature, forabout ten to eighteen days. Individual, matured somatic embryos withwell-defined scutellum and coleoptile are transferred to PHI-F embryogermination medium and incubated at 28° C. in the light (about 80 μEfrom cool white or equivalent fluorescent lamps). In seven to ten days,regenerated plants, about 10 cm tall, are potted in horticultural mixand hardened-off using standard horticultural methods.

Media for Plant Transformation:

-   -   1. PHI-A: 4 g/L CHU basal salts, 1.0 mL/L 1000× Eriksson's        vitamin mix, 0.5 mg/L thiamin HCl, 1.5 mg/L 2,4-D, 0.69 g/L        L-proline, 68.5 g/L sucrose, 36 g/L glucose, pH 5.2. Add 100 μM        acetosyringone (filter-sterilized).    -   2. PHI-B: PHI-A without glucose, increase 2,4-D to 2 mg/L,        reduce sucrose to 30 g/L and supplemented with 0.85 mg/L silver        nitrate (filter-sterilized), 3.0 g/L GELRITE®, 100 μM        acetosyringone (filter-sterilized), pH 5.8.    -   3. PHI-C: PHI-B without GELRITE® and acetosyringonee, reduce        2,4-D to 1.5 mg/L and supplemented with 8.0 g/L agar, 0.5 g/L        2-[N-morpholino]ethane-sulfonic acid (MES) buffer, 100 mg/L        carbenicillin (filter-sterilized).    -   4. PHI-D: PHI-C supplemented with 3 mg/L bialaphos        (filter-sterilized).    -   5. PHI-E: 4.3 g/L of Murashige and Skoog (MS) salts, (GIBCO, BRL        11117-074), 0.5 mg/L nicotinic acid, 0.1 mg/L thiamine HCl, 0.5        mg/L pyridoxine HCl, 2.0 mg/L glycine, 0.1 g/L myo-inositol, 0.5        mg/L zeatin (Sigma, Cat. No. Z-0164), 1 mg/L indole acetic acid        (IAA), 26.4 μg/L abscisic acid (ABA), 60 g/L sucrose, 3 mg/L        bialaphos (filter-sterilized), 100 mg/L carbenicillin        (filter-sterilized), 8 g/L agar, pH 5.6.    -   6. PHI-F: PHI-E without zeatin, IAA, ABA; reduce sucrose to 40        g/L; replacing agar with 1.5 g/L GELRITE®; pH 5.6.

Plants can be regenerated from the transgenic callus by firsttransferring clusters of tissue to N6 medium supplemented with 0.2 mgper liter of 2,4-D. After two weeks the tissue can be transferred toregeneration medium (Fromm et al., Bio/Technology 8:833-839 (1990)).

Transgenic TO plants can be regenerated and their phenotype determined.T1 seed can be collected.

T1 plants can be grown under nitrogen limiting conditions, for example 1mM nitrate, and analyzed for phenotypic changes. The followingparameters can be quantified using image analysis: plant area, volume,growth rate and color analysis can be collected and quantified.Overexpression constructs that result in an alteration, compared tosuitable control plants, in greenness (green color bin), yield, growthrate, biomass, fresh or dry weight at maturation, fruit or seed yield,total plant nitrogen content, fruit or seed nitrogen content, nitrogencontent in vegetative tissue, free amino acid content in the wholeplant, free amino acid content in vegetative tissue, free amino acidcontent in the fruit or seed, protein content in the fruit or seed, orprotein content in a vegetative tissue can be considered evidence thatthe Arabidopsis lead gene functions in maize to enhance tolerance tonitrogen deprivation (increased nitrogen tolerance).

Furthermore, a recombinant DNA construct containing a validatedArabidopsis gene can be introduced into a maize inbred line either bydirect transformation or introgression from a separately transformedline.

Example 14A Preparation of Expression Vector for Transformation of MaizeLines with Validated Candidate Arabidopsis Gene (At5q50930) UsingAgrobacterium

Using the INVITROGEN™ GATEWAY® technology, an LR Recombination Reactionwas performed with the GATEWAY® entry clone containing the ArabidopsisInt2-2 (described in Example 5), entry clone PHP23112 (SEQ ID NO:14),entry clone PHP20234 (SEQ ID NO:9; FIG. 9) and destination vectorPHP22655 (SEQ ID NO:10) to generate the precursor plasmid PHP28699.Likewise, an LR Recombination Reaction was performed with the GATEWAY®entry clone containing the Arabidopsis Int2-2 (described in Example 5),entry clone PHP23112 (SEQ ID NO:14), entry clone PHP20234 (SEQ ID NO:9;FIG. 9) and destination vector PHP22655 (SEQ ID NO:10) to generate theprecursor plasmid PHP28700. PHP28699 and PHP28700 each contain thefollowing expression cassettes:

1. Ubiquitin promoter::moPAT::PinII terminator cassette expressing thePAT herbicide resistance gene used for selection during thetransformation process.

2. LTP2 promoter::DS-RED2::PinII terminator cassette expressing theDS-RED color marker gene used for seed sorting.

In addition, PHP28699 contains the Ubiquitin promoten:Int2-2::PinIIterminator cassette overexpressing the Arabidopsis LNT2-2, and PHP28700contains the Ubiquitin promoter:Int2-3::PinII terminator cassetteoverexpressing the Arabidopsis LNT2-3.

Example 14B Transformation of Maize Lines with Validated CandidateArabidopsis Gene (At5g50930) Using Agrobacterium

The LNT2-2 expression cassette present in vector PHP28699 (described inExample 14A) can be introduced into a maize inbred line, or atransformable maize line derived from an elite maize inbred line, usingAgrobacterium-mediated transformation as described in Examples 12 and13. The same procedures can also be used to introduce the LNT2-3expression cassette present in PHP28700 into a maize inbred line, or atransformable maize line derived from an elite maize inbred line.

Expression vector PHP28699 can be electroporated into the LBA4404Agrobacterium strain containing vector PHP10523 (SEQ ID NO:7, FIG. 7) tocreate the co-integrate vector PHP28841, which contains the Int2-2expression cassette. The co-integrate vector is formed by recombinationof the two plasmids, PHP28699 and PHP10523, through the COSrecombination sites contained on each vector and contains the same threeexpression cassettes as above (Example 14A) in addition to other genes(TET, TET, TRFA, ORI terminator, CTL, ORI V, VIR C1, VIR C2, VIR G, VIRB) needed for the Agrobacterium strain and the Agrobacterium-mediatedtransformation. Similarly, expression vector PHP28700 can beelectroporated into the LBA4404 Agrobacterium strain containing vectorPHP10523 (SEQ ID NO:7, FIG. 7) to create the co-integrate vectorPHP28840, which contains the Int2-3 expression cassette. Theelectroporation protocol in, but not limited to, Example 12 may be used.

Example 15 Preparation of the Destination Vector PHP23236 forTransformation into Gaspe Flint derived Maize Lines

Destination vector PHP23236 (FIG. 6; SEQ ID NO:6) was obtained bytransformation of Agrobacterium strain LBA4404 containing PHP10523 (FIG.7; SEQ ID NO:7) with vector PHP23235 (FIG. 8; SEQ ID NO:8) and isolationof the resulting co-integration product.

Destination vector PHP23236 can be used in a recombination reaction withan entry clone, as described in Example 16, to create a maize expressionvector for transformation of Gaspe Flint derived maize lines.

Example 16 Preparation of Expression Constructs for Transformation intoGaspe Flint Derived Maize Lines

Using the INVITROGEN™ GATEWAY® LR Recombination technology, the sameentry clones described in Example 5 can be used to directionally clonethe expression cassettes into the GATEWAY® destination vector PHP23236(SEQ ID NO:6; FIG. 6) to create corresponding expression vectors.Expression vectors PHP29694 and PHP29689 contain Int2-2 (SEQ ID NO:29)and Int2-3 (SEQ ID NO:31), respectively. Each expression vector containsthe cDNA of interest under control of the UBI promoter and is a T-DNAbinary for Agrobacterium-mediated transformation into maize asdescribed, but not limited to, the examples described herein.

Example 17A Transformation of Gaspe Flint Derived Maize Lines withValidated Candidate Arabidopsis Gene (At5g50930)

Maize plants can be transformed to overexpress the Arabidopsis At5g50930gene (and the corresponding homologs from other species) in order toexamine the resulting phenotype. Expression constructs such as the onedescribed in Example 16 may be used.

Recipient Plants

Recipient plant cells can be from a uniform maize line having a shortlife cycle (“fast cycling”), a reduced size, and high transformationpotential. Typical of these plant cells for maize are plant cells fromany of the publicly available Gaspe Flint (GF) line varieties. Onepossible candidate plant line variety is the F1 hybrid of GF×QTM (QuickTurnaround Maize, a publicly available form of Gaspe Flint selected forgrowth under greenhouse conditions) disclosed in Tomes et al. (U.S.application Ser. No. 10/367,416 filed Feb. 13, 2003; U.S. PatentPublication No. 2003/0221212 A1 published Nov. 27, 2003). Transgenicplants obtained from this line are of such a reduced size that they canbe grown in four inch pots (¼ the space needed for a normal sized maizeplant) and mature in less than 2.5 months. (Traditionally 3.5 months isrequired to obtain transgenic T0 seed once the transgenic plants areacclimated to the greenhouse.) Another suitable line includes but is notlimited to a double haploid line of GS3 (a highly transformableline)×Gaspe Flint. Yet another suitable line is a transformable elitemaize inbred line carrying a transgene which causes early flowering,reduced stature, or both.

Transformation Protocol

Any suitable method may be used to introduce the transgenes into themaize cells, including but not limited to inoculation type proceduresusing Agrobacterium based vectors (see, for example, Examples 12 and13). Transformation may be performed on immature embryos of therecipient (target) plant.

Precision Growth and Plant Tracking

The event population of transgenic (T0) plants resulting from thetransformed maize embryos is grown in a controlled greenhouseenvironment using a modified randomized block design to reduce oreliminate environmental error. A randomized block design is a plantlayout in which the experimental plants are divided into groups (e.g.,thirty plants per group), referred to as blocks, and each plant israndomly assigned a location within the block.

For a group of thirty plants, twenty-four transformed, experimentalplants and six control plants (plants with a set phenotype)(collectively, a “replicate group”) are placed in pots which arearranged in an array (a.k.a. a replicate group or block) on a tablelocated inside a greenhouse. Each plant, control or experimental, israndomly assigned to a location within the block which is mapped to aunique, physical greenhouse location as well as to the replicate group.Multiple replicate groups of thirty plants each may be grown in the samegreenhouse in a single experiment. The layout (arrangement) of thereplicate groups should be determined to minimize space requirements aswell as environmental effects within the greenhouse. Such a layout maybe referred to as a compressed greenhouse layout.

An alternative to the addition of a specific control group is toidentify those transgenic plants that do not express the gene ofinterest. A variety of techniques such as RT-PCR can be applied toquantitatively assess the expression level of the introduced gene. TOplants that do not express the transgene can be compared to those whichdo.

Each plant in the event population is identified and tracked throughoutthe evaluation process, and the data gathered from that plant isautomatically associated with that plant so that the gathered data canbe associated with the transgene carried by the plant. For example, eachplant container can have a machine readable label (such as a UniversalProduct Code (UPC) bar code) which includes information about the plantidentity, which in turn is correlated to a greenhouse location so thatdata obtained from the plant can be automatically associated with thatplant.

Alternatively any efficient, machine readable, plant identificationsystem can be used, such as two-dimensional matrix codes or even radiofrequency identification tags (RFID) in which the data is received andinterpreted by a radio frequency receiver/processor. See U.S.application Ser. No. 10/324,288 filed Dec. 19, 2002 (U.S. PatentPublication No. 2004/0122592 A1 published Jun. 24, 2004), incorporatedherein by reference.

Phenotypic Analysis Using Three-Dimensional Imaging

Each greenhouse plant in the T0 event population, including any controlplants, is analyzed for agronomic characteristics of interest, and theagronomic data for each plant is recorded or stored in a manner so thatit is associated with the identifying data (see above) for that plant.Confirmation of a phenotype (gene effect) can be accomplished in the T1generation with a similar experimental design to that described above.

The T0 plants are analyzed at the phenotypic level using quantitative,non-destructive imaging technology throughout the plant's entiregreenhouse life cycle to assess the traits of interest. In anembodiment, a digital imaging analyzer is used for automaticmulti-dimensional analyzing of total plants. The imaging may be doneinside the greenhouse. Two camera systems, located at the top and side,and an apparatus to rotate the plant, are used to view and image plantsfrom all sides. Images are acquired from the top, front and side of eachplant. All three images together provide sufficient information toevaluate, for example, the biomass, size, and morphology of each plant.

Due to the change in size of the plants from the time the first leafappears from the soil to the time the plants are at the end of theirdevelopment, the early stages of plant development are In an embodimentdocumented with a higher magnification from the top. This imaging may beaccomplished by using a motorized zoom lens system that is fullycontrolled by the imaging software.

In a single imaging analysis operation, the following events occur: (1)the plant is conveyed inside the analyzer area, rotated 360 degrees soits machine readable label can be read, and left at rest until itsleaves stop moving; (2) the side image is taken and entered into adatabase; (3) the plant is rotated 90 degrees and again left at restuntil its leaves stop moving, and (4) the plant is transported out ofthe analyzer.

Plants are allowed at least six hours of darkness per twenty four hourperiod in order to have a normal day/night cycle.

Imaging Instrumentation

Any suitable imaging instrumentation may be used, including but notlimited to light spectrum digital imaging instrumentation commerciallyavailable from LemnaTec GmbH of Wurselen, Germany. The images are takenand analyzed with a LemnaTec Scanalyzer HTS LT-0001-2 having a ½″ ITProgressive Scan IEE CCD imaging device. The imaging cameras may beequipped with a motor zoom, motor aperture, and motor focus. All camerasettings may be made using LemnaTec software. In an embodiment, theinstrumental variance of the imaging analyzer is less than about 5% formajor components and less than about 10% for minor components.

Software

The imaging analysis system comprises a LemnaTec HTS Bonit softwareprogram for color and architecture analysis and a server database forstoring data from about 500,000 analyses, including the analysis dates.The original images and the analyzed images are stored together to allowthe user to do as much reanalyzing as desired. The database can beconnected to the imaging hardware for automatic data collection andstorage. A variety of commercially available software systems (e.g.,Matlab, others) can be used for quantitative interpretation of theimaging data, and any of these software systems can be applied to theimage data set.

Conveyor System

A conveyor system with a plant rotating device may be used to transportthe plants to the imaging area and rotate them during imaging. Forexample, up to four plants, each with a maximum height of 1.5 m, areloaded onto cars that travel over the circulating conveyor system andthrough the imaging measurement area. In this case the total footprintof the unit (imaging analyzer and conveyor loop) is about 5 m×5 m.

The conveyor system can be enlarged to accommodate more plants at atime. The plants are transported along the conveyor loop to the imagingarea and are analyzed for up to 50 seconds per plant. Three views of theplant are taken. The conveyor system, as well as the imaging equipment,should be capable of being used in greenhouse environmental conditions.

Illumination

Any suitable mode of illumination may be used for the image acquisition.For example, a top light above a black background can be used.Alternatively, a combination of top- and backlight using a whitebackground can be used. The illuminated area should be housed to ensureconstant illumination conditions. The housing should be longer than themeasurement area so that constant light conditions prevail withoutrequiring the opening and closing or doors. Alternatively, theillumination can be varied to cause excitation of either transgene(e.g., green fluorescent protein (GFP), red fluorescent protein (RFP))or endogenous (e.g. Chlorophyll) fluorophores).

Biomass Estimation Based on Three-Dimensional Imaging

For best estimation of biomass the plant images should be taken from atleast three axes, In an embodiment the top and two side (sides 1 and 2)views. These images are then analyzed to separate the plant from thebackground, pot and pollen control bag (if applicable). The volume ofthe plant can be estimated by the calculation:

Volume(voxels)=√{square root over (TopArea(pixels))}×√{square root over(Side1Area(pixels))}×√{square root over (Side2Area(pixels))}

In the equation above the units of volume and area are “arbitraryunits”. Arbitrary units are entirely sufficient to detect gene effectson plant size and growth in this system because what is desired is todetect differences (both positive-larger and negative-smaller) from theexperimental mean, or control mean. The arbitrary units of size (e.g.area) may be trivially converted to physical measurements by theaddition of a physical reference to the imaging process. For instance, aphysical reference of known area can be included in both top and sideimaging processes. Based on the area of these physical references aconversion factor can be determined to allow conversion from pixels to aunit of area such as square centimeters (cm²). The physical referencemay or may not be an independent sample. For instance, the pot, with aknown diameter and height, could serve as an adequate physicalreference.

Color Classification

The imaging technology may also be used to determine plant color and toassign plant colors to various color classes. The assignment of imagecolors to color classes is an inherent feature of the LemnaTec software.With other image analysis software systems color classification may bedetermined by a variety of computational approaches.

For the determination of plant size and growth parameters, a usefulclassification scheme is to define a simple color scheme including twoor three shades of green (In an embodiment hues 50-66, see FIG. 12) and,in addition, a color class for chlorosis, necrosis and bleaching, shouldthese conditions occur. A background color class which includes nonplant colors in the image (for example pot and soil colors) is also usedand these pixels are specifically excluded from the determination ofsize. The plants are analyzed under controlled constant illumination sothat any change within one plant over time, or between plants ordifferent batches of plants (e.g. seasonal differences) can bequantified.

In addition to its usefulness in determining plant size growth, colorclassification can be used to assess other yield component traits. Forthese other yield component traits additional color classificationschemes may be used. For instance, the trait known as “staygreen”, whichhas been associated with improvements in yield, may be assessed by acolor classification that separates shades of green from shades ofyellow and brown (which are indicative of senescing tissues). Byapplying this color classification to images taken toward the end of theT0 or T1 plants' life cycle, plants that have increased amounts of greencolors relative to yellow and brown colors (expressed, for instance, asGreen/Yellow Ratio) may be identified. Plants with a significantdifference in this Green/Yellow ratio can be identified as carryingtransgenes which impact this important agronomic trait.

The skilled plant biologist will recognize that other plant colors arisewhich can indicate plant health or stress response (for instanceanthocyanins), and that other color classification schemes can providefurther measures of gene action in traits related to these responses.

Plant Architecture Analysis

Transgenes which modify plant architecture parameters may also beidentified using the present invention, including such parameters asmaximum height and width, internodal distances, angle between leaves andstem, number of leaves starting at nodes, and leaf length. The LemnaTecsystem software may be used to determine plant architecture as follows.The plant is reduced to its main geometric architecture in a firstimaging step and then, based on this image, parameterized identificationof the different architecture parameters can be performed. Transgenesthat modify any of these architecture parameters either singly or incombination can be identified by applying the statistical approachespreviously described.

Pollen Shed Date

Pollen shed date is an important parameter to be analyzed in atransformed plant, and may be determined by the first appearance on theplant of an active male flower. To find the male flower object, theupper end of the stem is classified by color to detect yellow or violetanthers. This color classification analysis is then used to define anactive flower, which in turn can be used to calculate pollen shed date.

Alternatively, pollen shed date and other easily visually detected plantattributes (e.g., pollination date, first silk date) can be recorded bythe personnel responsible for performing plant care. To maximize dataintegrity and process efficiency, this data is tracked by utilizing thesame barcodes utilized by the LemnaTec light spectrum digital analyzingdevice. A computer with a barcode reader, a palm device, or a notebookPC may be used for ease of data capture recording time of observation,plant identifier, and the operator who captured the data.

Orientation of the Plants

Mature maize plants grown at densities approximating commercial plantingoften have a planar architecture. That is, the plant has a clearlydiscernable broad side, and a narrow side. The image of the plant fromthe broadside is determined. To each plant a well defined basicorientation is assigned to obtain the maximum difference between thebroadside and edgewise images. The top image is used to determine themain axis of the plant, and an additional rotating device is used toturn the plant to the appropriate orientation prior to starting the mainimage acquisition.

Example 17B Transformation of Gaspe Flint Derived Maize Lines with MaizeHomolog

Using the INVITROGEN™ GATEWAY® LR Recombination technology, an entryclone may be created for the maize homolog (SEQ ID NO:17) (see Example 5for entry clone preparation) and can be directionally cloned into theGATEWAY® destination vector PHP23236 (SEQ ID NO:6; FIG. 6) to create anexpression vector PHP30115. This expression vector now contains the cDNAof interest under control of the UBI promoter and is a T-DNA binary forAgrobacterium-mediated transformation into maize as described, but notlimited to, the examples described herein.

Example 18 Screening of Gaspe Flint Derived Maize Lines Under Optimaland Reduced Nitrogen Conditions

Transgenic plants contain two or three doses of Gaspe Flint-3 with onedose of GS3 (GS3/(Gaspe-3)2× or GS3/(Gaspe-3)3×) and segregate 1:1 for adominant transgene. Transgenic plants containing PHP29689 (expressioncassette=Int2-3) were planted in 100% Turface in classic 200 pots.Plants were watered with 1.0 mM KNO₃ growth medium (see FIG. 13) untilsegregant determination. At 8 DAP (days after planting), seedlings wererandomized and placed equally into respective treatment groups. Twotreatments were applied: optimal (6.5 mMol KNO₃) and reduced nitrogen(1.0 mMol KNO₃), twice daily until 13 DAP. The daily irrigation scheduleconsisted of a 9:00 AM, 12:00 PM, and 3:00 PM nutrient watering for 3minutes (156 ml) between 13 and 24 DAP. A fourth watering was added at5:00 AM on 25 DAP, and a fifth watering was added at 5:00 PM on 31 DAP.pH was monitored at least three times weekly for each table, and days toemergence and days to shed were recorded. Imaging to assess surface areaaccumulation, specific growth rates (sgr), and changes in color, wasperformed for each plant three times per week (Monday, Wednesday, andFriday). Plants were sampled for ELISA MOPAT on 8 DAP and for expressionand metabolic profiling analysis on 35 DAP. Fresh weight data wasobtained from harvested tissue, obtained at 37 DAP, and the harvestedtissue was then oven dried (70° C. for 120 hrs.) to obtain dry weightdata.

Four events for PHP29689 were evaluated (FIGS. 16A-16I). The probabilityof a greater Student's t test was calculated for each transgenic meancompared to the appropriate null mean (either segregant null orconstruct null). A minimum (P<t) of 0.1 was used as a cut off. Table 5shows the variables for each event that were significantly increased, ascompared to the segregant nulls.

TABLE 5 PHP29689 event summary Event Reduced nitrogen Optimal nitrogenEA2391.314.1.5 % light green end % light green end exponentialexponential % light green harvest Ear diameter day Ear dry weight Totalarea harvest day Ear fresh weight Days to shed Maximum total areaSpecific growth rate Shoot fresh rate EA2391.314.1.6 Total area end %light green end exponential exponential Total area harvest day % lightgreen harvest day Maximum total area Total area end exponential Shootdry weight Total area harvest day Shoot fresh weight Maximum total areaShoot + ear dry weight Specific growth rate Shoot + ear fresh weightShoot dry weight Stalk + ear diameter Shoot fresh weight Shoot + ear dryweight Shoot + ear fresh weight EA2391.314.1.8 Days to shed % lightgreen end Specific growth rate exponential Shoot fresh weight % lightgreen harvest day Shoot + ear fresh weight Days to shed Specific growthrate EA2391.314.1.9 % light green end exponential % light green harvestday Total area harvest day Maximum total area Specific growth rate

When all events were considered relative to the construct null (FIGS.17A-17C), the construct, on average, evinced a significant increase overthe construct null for a number of variables (data summarized in Table6).

TABLE 6 PHP29689 construct summary Reduced nitrogen Optimal nitrogen %light green harvest day % light green end exponential Total area harvestday % light green harvest day Days to shed Total area end exponentialMax total area Total area harvest day Specific growth rate Days to shedShoot fresh weight Max total area Specific growth rate Shoot dry weightShoot fresh weight Shoot + ear dry weight Shoot + ear fresh weight

Example 19 Yield Analysis of Maize Lines with the Arabidopsis Lead Genes

Transgenic plants, either inbreds or topeross hybrids, can undergo morevigorous field-based experiments to study yield enhancement and/orstability under nitrogen limiting and non-limiting conditions. Forexample, yield analysis can be done to determine whether plants thatcontain a validated Arabidopsis Int2-2 or Int2-3 gene have animprovement in yield performance (under nitrogen limiting ornon-limiting conditions), when compared to the control (or reference)plants, that are either construct null or wild-type. Nitrogen limitingconditions are provided by a combination of previous fertility practicesin which nitrogen is applied at reduced levels for one or more yearswhere corn or an alternative crop is grown and the seed crop is removedeach season. Under such conditions, a low nitrogen (LN) environmentconsists of a less than normal amount of nitrogen fertilizer applied inearly spring or summer, whereas a normal nitrogen (NN) environmentconsists of adding adequate nitrogen for normal yields, based on soiltest standards established for specific growing areas by Federal andState Extension services.

Corn hybrid testcrosses, containing either the validated ArabidopsisInt2-2 or Int2-3 gene, and their controls were grown in LN and NNenvironments in Woodland, Calif., and in Johnston, Iowa, and yield wasassessed. Yield reduction was observed in LN environments compared tothat obtained in NN environments. Yields of the corn hybrid testcrosses,containing either the validated Arabidopsis Int2-2 or Int2-3 gene, werecompared to that of the construct nulls. The results of these yieldtrials are shown in FIGS. 18-21.

Individual events of plants containing PHP28840 (expressioncassette=Int2-3) showed significantly increased yield under LNconditions in 2007 for events E6919.105.1.11 and E6919.105.1.21 inWoodland, while the E6919.105.1.21 event tested in Johnston in 2007 wasnumerically higher in yield. Similar testing in 2008 revealedsignificantly improved yield for event E6919.105.1.21 in both Woodlandand Johnston and for events E6919.105.1.2 and E6919.105.1.24, inWoodland and in Johnston, respectively. The results forPHP28840-containing plants under low nitrogen conditions are shown inFIG. 18

Under normal nitrogen (NN) treatments, event E6919.105.1.11 was similarin yield to the construct null (not statistically different) in bothWoodland and Johnston in 2007, suggesting that under higher nitrogenlevels, this event retains high yield potential. A similar result wasobtained in 2008 at the Woodland location. In contrast, eventE3919.105.1.11 in Johnston in 2008 and events E6919.105.1.21 andE6919.105.1.24 in Johnston in 2007 and 2008 had significantly loweryields. The results for PHP28840-containing plants under normal nitrogenconditions are shown in FIG. 20.

Individual events of plants containing PHP28841 (expressioncassette=Int2-2) showed a statistically significant increase in yieldfor events E6919.106.1.17 and E6919.106.1.3 under LN conditions inWoodland in 2007. However, in Johnston in 2007 under LN conditions,event E6919.106.1.3 showed significantly lower yields, and yields werenot collected for event E6919.106.1.17. The results forPHP28841-containing plants under low nitrogen (LN) conditions are shownin FIG. 19.

Under normal nitrogen (NN) treatments, E6919.106.1.17 had numericallyhigher yields in both Woodland and Johnston in 2007, as compared to theconstruct null, while event E6919.106.1.3 showed a significant increasein yield in Woodland in 2007 and a numerical increase in Johnston in2007. Events E6919.106.1.22 and E619.106.1.8 showed significantdecreases in yield in Woodland. The results for PHP28841-containingplants under normal nitrogen (NN) conditions are shown in FIG. 21.

Example 20 NUE Maize Seedling Assay

Seed of transgenic events (having construct PHP28841 or PHP28840) wereseparated into transgene (heterozygous) and null seed using a seed colormarker. Two different random assignments of treatments were made to eachblock of 54 pots, which were arranged 6 rows by 9 columns using 9replicates of all treatments. In one case, 4 null seed of 5 events ofthe same construct were mixed and used as a bulked control forcomparisons of the 5 positive events in this block, making up 6treatment combinations in each block. In the second case, 3 transgenicpositive treatments and their corresponding nulls were randomly assignedto the 54 pots of the block, making 6 treatment combinations (3 positiveand corresponding nulls) for each block, containing 9 replicates of alltreatment combinations. In the first case, transgenic parameters werecompared to a bulked construct null; in the second case, transgenicparameters were compared to the corresponding event null. In cases wherethere were 10, 15, or 20 events per construct, the events were assignedin groups of 5 events and the variances were calculated for each blockof 54 pots. However, the block null means were pooled across blocksbefore transgenic mean comparisons were made.

For each treatment, two seeds were planted in a 4 inch square potcontaining Turface, on 8 inch, staggered centers. The pots were wateredfour times each day with a solution containing the following nutrients:1 mM CaCl₂, 2 mM MgSO₄, 0.5 mM KH₂PO₄, 83 ppm Sprint330, 3 mM KCl, 1 mMKNO₃, 1 μM ZnSO₄, 1 μM MnCl₂, 3 μM H₃BO₄, 0.1 μM CuSO₄, and 0.1 μMNaMoO₄.

After emergence, the plants were thinned to one seed per pot. Treatmentswere routinely planted on a Monday, and the plants emerged the followingFriday. The plants were then harvested 18 days after planting. Atharvest, plants were removed from the pots, and the Turface was washedfrom the roots. The roots were separated from the shoot, placed in apaper bag and dried at 70° C. for 70 hr. The dried plant parts (rootsand shoots) were weighed and placed in a 50 ml conical tube withapproximately 20 5/32 inch steel balls and then ground by shaking in apaint shaker. Approximately, 30 mg of the ground tissue (weight recordedfor later adjustment) was hydrolyzed in 2 ml of 20% H₂O₂ and 6M H₂SO₄for 30 min at 170° C. After cooling, water was added to 20 ml, and thesolution was mixed thoroughly. A 50 μl aliquot was removed and added to950 μl M Na₂CO₃. The ammonia in this solution was used to estimate totalreduced plant nitrogen by placing 100 μl of this solution intoindividual wells of a 96 well plate and then adding 50 μl of OPAsolution. Fluorescence, excitation=360 nM/emission=530 nM, wasdetermined and compared to NH₄Cl standards dissolved in a similarsolution and treated with OPA solution.

The following solutions were used in the aforementioned experiments:

OPA solution−5 μl Mercaptoethanol+1 ml OPA stock solution(make fresh,daily)

OPA stock−50 mg o-phthadialdehyde(OPA—Sigma #P0657)dissolved in 1.5 mlmethanol+4.4 ml 1M Borate buffer pH9.5(3.09 g H₃BO₄+1 g NaOH in 50 mlwater)+0.55 ml 20% SDS(made fresh weekly)

The following parameters were measured, and the means were compared tonull mean parameters using a Student's t test: SPAD (greenness), stemdiameter, root dry weight, shoot dry weight, total dry weight, and plantN concentration. Variance was calculated within each block using anearest neighbor calculation as well as by Analysis of Variance (ANOVA)using a completely random design (CRD) model. An overall treatmenteffect for each block was calculated using an F statistic, by dividingoverall block treatment mean square by the overall block error meansquare. The probability of a greater Student's t test was calculated foreach transgenic mean compared to the appropriate null (either constructbulked or individual event null mean) mean. A minimum (P<t) of 0.1 wasused as a cut off.

The results of the NUE seedling assay for the PHP28840 (expressioncassette=Int2-3) and PHP28841 (expression cassette=Int2-2) constructsare shown in FIG. 22. Event E6919.105.1.21, which contains theUBI:Int2-3 expression cassette, showed a statistically significantincrease in the following: shoot dry weight, nitrogen concentration, andtotal N. Another event with the UBI:Int2-3 expression cassette and fourout of six events with the UBI:Int2-2 expression cassette evinced astatistically significant increase in plant N concentration. Inaddition, two out of six events containing the UBI:Int2-2 expressioncassette showed a statistically significant increase in total N.

Example 21 Transformation and Evaluation of Soybean with SoybeanHomologs of Validated Lead Genes

Based on homology searches, one or several candidate soybean homologs ofvalidated Arabidopsis leads can be identified and also be assessed fortheir ability to enhance tolerance to nitrogen limiting conditions insoybean. Vector construction, plant transformation and phenotypicanalysis will be similar to that in previously described Examples.

Example 22 Transformation and Evaluation of Maize with Maize Homologs ofValidated Lead Genes

Based on homology searches, one or several candidate maize homologs ofvalidated Arabidopsis lead genes can be identified (e.g., SEQ ID NOs:18and 20) and also be assessed for their ability to enhance tolerance tonitrogen limiting conditions in maize. Vector construction, planttransformation and phenotypic analysis can be similar to that inpreviously described Examples.

Example 23 Transformation of Arabidopsis with Maize and Soybean Homologsof Validated Lead Genes

Soybean and maize homologs to validated Arabidopsis lead genes can betransformed into Arabidopsis under control of the 35S promoter andassayed for leaf area and green color bin accumulation when grown on lownitrogen medium. Vector construction and plant transformation can be asdescribed in the examples herein. Assay conditions, data capture anddata analysis can be similar to that in previously described Examples.

What is claimed is:
 1. A plant comprising in its genome a recombinantDNA construct comprising a polynucleotide operably linked to at leastone regulatory element, wherein said polynucleotide encodes apolypeptide having an amino acid sequence of at least 50% sequenceidentity, based on the Clustal V method of alignment, when compared toSEQ ID NO:18, 20, 24, 26, 28, 30, or 32, and wherein said plant exhibitsincreased nitrogen stress tolerance when compared to a control plant notcomprising said recombinant DNA construct.
 2. The plant of claim 1,wherein the plant is a maize plant or a soybean plant.
 3. A plantcomprising in its genome a recombinant DNA construct comprising: (a) apolynucleotide operably linked to at least one regulatory element,wherein said polynucleotide encodes a polypeptide having an amino acidsequence of at least 50% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO: 18, 20, 24, 26, 28, 30,or 32; or (b) a suppression DNA construct comprising at least oneregulatory element operably linked to: (i) all or part of: (A) a nucleicacid sequence encoding a polypeptide having an amino acid sequence of atleast 50% sequence identity, based on the Clustal V method of alignment,when compared to SEQ ID NO: 18, 20, 24, 26, 28, 30, or 32, or (B) a fullcomplement of the nucleic acid sequence of (b)(i)(A); or (ii) a regionderived from all or part of a sense strand or antisense strand of atarget gene of interest, said region having a nucleic acid sequence ofat least 50% sequence identity, based on the Clustal V method ofalignment, when compared to said all or part of a sense strand orantisense strand from which said region is derived, and wherein saidtarget gene of interest encodes an LNT2 polypeptide, and wherein saidplant exhibits an alteration of at least one agronomic characteristicwhen compared to a control plant not comprising said recombinant DNAconstruct.
 4. The plant of claim 3, wherein the plant is a maize plantor a soybean plant.
 5. The plant of claim 3, wherein said plant exhibitssaid alteration of said at least one agronomic characteristic whencompared, under nitrogen limiting conditions, to said control plant notcomprising said recombinant DNA construct.
 6. The plant of claim 5,wherein the plant is a maize plant or a soybean plant.
 7. The plant ofclaim 3, wherein said at least one agronomic characteristic is selectedfrom the group consisting of greenness, yield, growth rate, biomass,fresh weight at maturation, dry weight at maturation, fruit yield, seedyield, total plant nitrogen content, fruit nitrogen content, seednitrogen content, nitrogen content in vegetative tissue, whole plantamino acid content, vegetative tissue free amino acid content, fruitfree amino acid content, seed free amino acid content, total plantprotein content, fruit protein content, seed protein content, proteincontent in a vegetative tissue, drought tolerance, nitrogen uptake,resistance to root lodging, harvest index, stalk lodging, plant height,ear height, and ear length.
 8. The plant of claim 7, wherein the plantis a maize plant or a soybean plant.
 9. The plant of claim 3, whereinsaid plant exhibits an increase of said at least one agronomiccharacteristic when compared to said control plant.
 10. The plant ofclaim 9, wherein the plant is a maize plant or a soybean plant.
 11. Amethod of increasing nitrogen stress tolerance in a plant, comprising:(a) introducing into a regenerable plant cell a recombinant DNAconstruct comprising a polynucleotide operably linked to at least oneregulatory sequence, wherein the polynucleotide encodes a polypeptidehaving an amino acid sequence of at least 50% sequence identity, basedon the Clustal V method of alignment, when compared to SEQ ID NO: 18,20, 24, 26, 28, 30, or 32; and (b) regenerating a transgenic plant fromthe regenerable plant cell after step (a), wherein the transgenic plantcomprises in its genome the recombinant DNA construct and exhibitsincreased nitrogen stress tolerance when compared to a control plant notcomprising the recombinant DNA construct.
 12. The method of claim 11,further comprising: (c) obtaining a progeny plant derived from thetransgenic plant, wherein said progeny plant comprises in its genome therecombinant DNA construct and exhibits increased nitrogen stresstolerance when compared to a control plant not comprising therecombinant DNA construct.
 13. A method of evaluating nitrogen stresstolerance in a plant, comprising: (a) introducing into a regenerableplant cell a recombinant DNA construct comprising a polynucleotideoperably linked to at least one regulatory sequence, wherein thepolynucleotide encodes a polypeptide having an amino acid sequence of atleast 50% sequence identity, based on the Clustal V method of alignment,when compared to SEQ ID NO: 18, 20, 24, 26, 28, 30, or 32; (b)regenerating a transgenic plant from the regenerable plant cell afterstep (a), wherein the transgenic plant comprises in its genome therecombinant DNA construct; and (c) evaluating the transgenic plant fornitrogen stress tolerance compared to a control plant not comprising therecombinant DNA construct.
 14. The method of claim 13, furthercomprising: (d) obtaining a progeny plant derived from the transgenicplant, wherein the progeny plant comprises in its genome the recombinantDNA construct; and (e) evaluating the progeny plant for nitrogen stresstolerance compared to a control plant not comprising the recombinant DNAconstruct.
 15. A method of evaluating nitrogen stress tolerance in aplant, comprising: (a) introducing into a regenerable plant cell arecombinant DNA construct comprising a polynucleotide operably linked toat least one regulatory sequence, wherein the polynucleotide encodes apolypeptide having an amino acid sequence of at least 50% sequenceidentity, based on the Clustal V method of alignment, when compared toSEQ ID NO: 18, 20, 24, 26, 28, 30, or 32; (b) regenerating a transgenicplant from the regenerable plant cell after step (a), wherein thetransgenic plant comprises in its genome the recombinant DNA construct;(c) obtaining a progeny plant derived from the transgenic plant, whereinthe progeny plant comprises in its genome the recombinant DNA construct;and (d) evaluating the progeny plant for nitrogen stress tolerancecompared to a control plant not comprising the recombinant DNAconstruct.
 16. A method of determining an alteration of an agronomiccharacteristic in a plant, comprising: (a) introducing into aregenerable plant cell a recombinant DNA construct comprising apolynucleotide operably linked to at least one regulatory sequence,wherein the polynucleotide encodes a polypeptide having an amino acidsequence of at least 50% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO: 18, 20, 24, 26, 28, 30,or 32; (b) regenerating a transgenic plant from the regenerable plantcell after step (a), wherein the transgenic plant comprises in itsgenome the recombinant DNA construct; and (c) determining whether thetransgenic plant exhibits an alteration of at least one agronomiccharacteristic when compared to a control plant not comprising therecombinant DNA construct.
 17. The method of claim 16, furthercomprising: (d) obtaining a progeny plant derived from the transgenicplant, wherein the progeny plant comprises in its genome the recombinantDNA construct; and (e) determining whether the progeny plant exhibits analteration of at least one agronomic characteristic when compared to acontrol plant not comprising the recombinant DNA construct.
 18. Themethod of claim 16, wherein said determining step (c) comprisesdetermining whether the transgenic plant exhibits an alteration of atleast one agronomic characteristic when compared, under nitrogenlimiting conditions, to a control plant not comprising the recombinantDNA construct.
 19. The method of claim 17, wherein said determining step(e) comprises determining whether the progeny plant exhibits analteration of at least one agronomic characteristic when compared, undernitrogen limiting conditions, to a control plant not comprising therecombinant DNA construct.
 20. A method of determining an alteration ofan agronomic characteristic in a plant, comprising: (a) introducing intoa regenerable plant cell a recombinant DNA construct comprising apolynucleotide operably linked to at least one regulatory sequence,wherein the polynucleotide encodes a polypeptide having an amino acidsequence of at least 50% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO: 18, 20, 24, 26, 28, 30,or 32; (b) regenerating a transgenic plant from the regenerable plantcell after step (a), wherein the transgenic plant comprises in itsgenome the recombinant DNA construct; (c) obtaining a progeny plantderived from the transgenic plant, wherein the progeny plant comprisesin its genome the recombinant DNA construct; and (d) determining whetherthe progeny plant exhibits an alteration of at least one agronomiccharacteristic when compared to a control plant not comprising therecombinant DNA construct.
 21. The method of claim 20, wherein saiddetermining step (d) comprises determining whether the transgenic plantexhibits an alteration of at least one agronomic characteristic whencompared, under nitrogen limiting conditions, to a control plant notcomprising the recombinant DNA construct.
 22. A method of determining analteration of an agronomic characteristic in a plant, comprising: (a)introducing into a regenerable plant cell a suppression DNA constructcomprising at least one regulatory element operably linked to: (i) allor part of: (A) a nucleic acid sequence encoding a polypeptide having anamino acid sequence of at least 50% sequence identity, based on theClustal V method of alignment, when compared to SEQ ID NO:18, 20, 24,26, 28, 30, or 32, or (B) a full complement of the nucleic acid sequenceof (b)(i)(A); or (ii) a region derived from all or part of a sensestrand or antisense strand of a target gene of interest, said regionhaving a nucleic acid sequence of at least 50% sequence identity, basedon the Clustal V method of alignment, when compared to said all or partof a sense strand or antisense strand from which said region is derived,and wherein said target gene of interest encodes an LNT2 polypeptide;(b) regenerating a transgenic plant from the regenerable plant cellafter step (a), wherein the transgenic plant comprises in its genome thesuppression DNA construct; and (c) determining whether the transgenicplant exhibits an alteration of at least one agronomic characteristicwhen compared to a control plant not comprising the suppression DNAconstruct.
 23. The method of claim 22, wherein said determining step (c)comprises determining whether the transgenic plant exhibits analteration of at least one agronomic characteristic when compared, undernitrogen limiting conditions, to a control plant not comprising thesuppression DNA construct.
 24. The method of claim 22, furthercomprising: (d) obtaining a progeny plant derived from the transgenicplant, wherein the progeny plant comprises in its genome the suppressionDNA construct; and (e) determining whether the progeny plant exhibits analteration of at least one agronomic characteristic when compared to acontrol plant not comprising the suppression DNA construct.
 25. Themethod of claim 24, wherein said determining step (e) comprisesdetermining whether the progeny plant exhibits an alteration of at leastone agronomic characteristic when compared, under nitrogen limitingconditions, to a control plant not comprising the suppression DNAconstruct.
 26. A method of determining an alteration of an agronomiccharacteristic in a plant, comprising: (a) introducing into aregenerable plant cell a suppression DNA construct comprising at leastone regulatory element operably linked to: (i) all or part of: (A) anucleic acid sequence encoding a polypeptide having an amino acidsequence of at least 50% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO: 18, 20, 24, 26, 28, 30,or 32, or (B) a full complement of the nucleic acid sequence of(b)(i)(A); or (ii) a region derived from all or part of a sense strandor antisense strand of a target gene of interest, said region having anucleic acid sequence of at least 50% sequence identity, based on theClustal V method of alignment, when compared to said all or part of asense strand or antisense strand from which said region is derived, andwherein said target gene of interest encodes an LNT2 polypeptide; (b)regenerating a transgenic plant from the regenerable plant cell afterstep (a), wherein the transgenic plant comprises in its genome thesuppression DNA construct and exhibits an alteration of at least oneagronomic trait when compared to a control plant not comprising thesuppression DNA construct; (c) obtaining a progeny plant derived fromthe transgenic plant, wherein the progeny plant comprises in its genomethe suppression DNA construct; and (d) determining whether the progenyplant exhibits an alteration of at least one agronomic characteristicwhen compared to a control plant not comprising the suppression DNAconstruct.
 27. The method of claim 26, wherein said determining step (d)comprises determining whether the transgenic plant exhibits analteration of at least one agronomic characteristic when compared, undernitrogen limiting conditions, to a control plant not comprising therecombinant DNA construct.
 28. An isolated polynucleotide comprising:(i) a nucleic acid sequence encoding a polypeptide having an amino acidsequence of at least 85% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO:18, 24, or 26; or (ii) afull complement of the nucleic acid sequence of (i).
 29. The isolatedpolynucleotide of claim 28, wherein said polypeptide has an amino acidsequence of at least 90% sequence identity, based on the Clustal Vmethod of alignment, when compared to SEQ ID NO:18, 24, or
 26. 30. Theisolated polynucleotide of claim 28, wherein said polypeptide has anamino acid sequence of at least 95% sequence identity, based on theClustal V method of alignment, when compared to SEQ ID NO:18, 24, or 26.31. The isolated polynucleotide of claim 28, wherein the polypeptidesequence comprises SEQ ID NO:18, 24, or
 26. 32. The isolatedpolynucleotide of claim 28, wherein the nucleic acid sequence comprisesSEQ ID NO:17, 23, or 25.